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Carburetor Tuning

L

lee30bmw

Joined Feb 2011
23 Posts | 0+
Portland, OR
Hey guys,

I'm new to the forums but not to bikes or cars. Just to give you some background information, I'm a mechanic for a living and a mechanical engineering student. I'm not a carburetor expert as us new automotive guys are never trained to work on them, but I've gotten pretty familiar with them from owning many types of motorcycles, mostly 2 to 4 cylinder japanese bikes with cv carbs.

Anyways, I just bought a 1998 FE 600 E with the starter removed. It has a 'Big Gun' aftermarket exhaust. It pulls hard anything past 1/4 throttle, however, it usually takes about 20-30 kicks to start (main problem), has a bouncy/inconsistent idle, and pops during decel. All these sounded like it had a clogged idle jet, and possibly a clogged start jet. Correct me if I'm wrong.

I cleaned the carb and adjusted the float level (it was low) and it seemed to make a little bit of a difference, but it still dies during idle occasionally and is a absolute pain in the *** to start. I also checked the ignition timing with the TDC method (previous owner had already scribed new marks) and they were lined up. The spark plug is brand new.

Turning the idle mixture screw all the way in (richer) didn't have any affect on the idle, so I decided to investigate the situation further and check the jet sizing. The carburetor is Dellorto VHSB38 flat slide. I found a 185 main jet, 35 pilot jet, 50 start jet, 260 needle jet, k35 needle on position #3. According to the manual that came with the bike, it should have a 195 main, 40 pilot, 45 start, 270 needle jet and k51 needle.

After I read this, I thought 'wow these are all on the lean side.' Being that the bike seemed to only have trouble with 1/4 throttle and less, I decided to start messing with the pilot jet first (start jet was above factory size already). I stepped up to a 48 idle jet, and played around with the mixture screw. I can get the bike to start with but it still has trouble idling and takes more than enough kicks (~10-15).

With all that being said,
1)do you think I need to continue increasing my idle jet to get it to start and idle easier? 48 seems higher enough already based on the factory manual (45 stock)
2)the manual says the FE 600 is supposed to have a PHM 40 carburetor. Is having VHSB38 going to significantly change the jetting required? From fluid dynamics I know a smaller hole is going to increas air velocity, which decreases the pressure near the jet openings and would cause more fuel to be pulled into the venturi.
Perhaps this is the reason why the jetting was set smaller than the factory setting.
3)What bike is a VHSB38 out of? Whenever I search, it just brings up German webpages
 
By the way, I'm about 200-300 feet above sea level. Here's some pictures of the carb (before I adjusted the float level)

4a55603b4f406b452238f0bf10289a7c675ef737894f93ad2f3c787ebc436c2c5g.jpg


af8cf8ff53b2bd46e633abfc1b17d6692cf13f78901667f549d67671d35cdd285g.jpg


76265c407c1df774e654cac7a92c6c5831f7a972589727b5036d43acb3d752a45g.jpg
 
Yup, I've gone through there.

After reading more on the forums (theres actually another post made today), I've come to the conclusion that this is not the original carb for the bike. I can only hope that someone has dealt with this VHSB setup as far as jetting goes.
 
Hi lee

I have one 98 FE600E like yours, that bike actualy has a PHM40, I can't tell you the diferences between them and what it will do to your bike.
Beside the size the diference what I can see is that you have a pilot air srew not a pilot screw, so you don't control gas you control the air.
That been said, one thing that I think you should change on your jeting is the start jet, usualy is a 45 and maybe its too big. As you know all of this bikes comes on the rich side.
You can read in this site, in the posts and in the owners docs, there are several changes you can do in this bikes, but I would say to you there are some that could be important: first the stator may be it needs to be redone by sparks so it gives you a better spark at a low rpm and the timming done with a strobe light, and you could upgrade the sprocket cam to a steel one with a +04 automatic decompresion cam, this might need some work.
There are people that can help you more than I, if you whant I can point you those.

This bike is a great bike, it can be a lot of fun !!
Good luck

:cheers:
ZAGA
 
This is interesting..., I thought that the '98 models all used the round slide Dellortos. This particular carb came on the '96 models (including the 600) and I owned a '96 FE501 that I bought new. The manual specs for'98 (I'm guessing) refer to the 40mm round slide carb and not this one. The jetting it came with sounds about right as the 501 and 600 used about the same. I did a lot of messing around with mine and finally settled on a 35 pilot (stock), K35 needle raised one clip, stock start jet, and the air screw about 2-3/4-3 turns out. I also ended up taking 2mm off the bottom of the slide (I then had to raise the needle one position) to clean up the the off-idle transition.

This particular carb was used to lessen the throttle drag over the round slide models and the throttle turns considerably easier with this carb than with the round slide (I've had both) but htey only used it for 1 or 2 model years. Another difference is increased throttle responce over the 40mm round slide carbs - for example, my '96 FE501 was a lot "snappier" feeling than a friends '98 FC501 and felt like it had more power. The smaller venturi results in an increaseed intake velocity producing more suction which is why the smaller jets than with the round slide carb and quicker throttle responce.

The first thing I would do is go back to the stock jetting (35 pilot) and start with the needle clip and turn the air screw out to about 3 turns. The 260 needle jet sounds right also but it has been a long time since I had my '96 FE501. I used to have a '02 FE650 (40mm round slide) and it came with a 272 needle jet which I changed out for a 274 which made starting easier. I did play with the needle jet on my '96 501 but went back to the stock one. My dealer said that needles on these were kind of like black magic so I didn't try a K51. it is possible that this card came off a 400 does indeed need a richer needle jet (270?) since it seems like the main difference in jetting between the 400 and 501/600 was the needle jet.
 
Something I forgot to add, you may have a failing ignition which will cause the same symptoms. I had to replace the stator on my '02 FE650 as it became next to impossible to start and (if I remember right) also did a lot of back-firing on decelleration. When the SEM ignitions start to fail they produce a very weak, intermittant spark at low rpm (unlike the old Motoplats which just died completely) making starting very difficult. A new igniton may fix your problem.

Before you do anything else you should check the ignition timing as it may be off which will make the bike hard to start and can cause the back-firing. You will need a dial indicator to determine TDC as you cannot always rely on the timing marks, and then check it with a timing light after you get it started.
 
Thanks guys. I'm really impressed with the detailed information given. Not what I'm used to on the internet.

So first of all, for the ignition timing. I removed the stator cover and set the piston at TDC with a dial indicator. It appears that the previous owner has already tried to re-time the ignition. There was a new mark for TDC (a few degrees counterclockwise of the factory mark) follow by another mark that was much further advanced. I presume this is the 33 degrees (?) ahead mark that I had read in the wikidoc. While I haven't checked it dynamically with a timing light, the bike runs great off of idle, so I can atleast hope its close. Perhaps not close enough though....

I was thinking about putting a spark tester on the ignition wire as a simple check to see if I have an intermittent or weak spark while cranking. If this is the case, I will definentely need to look deeper into the ignition system. Who redoes the stators on this board, and what does it usually cost? I had heard something about this before...
 
Check your needle jet, They have a tendency to oval out. I needed a magnify glass to see it! It made a difference.
What does a plug reading show?
Is it hard to kick when you try to start it? Check your auto decomp on the cam, maybe the spring unwound as is a tendency with this device.
I have a PHM 40 on mine and still have an inconsistant idle and a slight pop on decel. I am interested in what you find out!
 
By the way, does anyone have an ignition timing write-up for the older husabergs like mine? I'm a little confused by the one on the wikidoc. It doesn't mention anything about using locating pin to line up the flywheel to the stator like my manual does. I figured this was because alot of the information of the wikidoc only applies to the 'newer' husabergs.

My stator cover doesn't have a timing plug that I can remove. I pressume you can you run the engine with the stator cover removed instead. Also, I can't wrap my head around why you need to set the gun to 72 degrees instead of 36 degrees becaues of waste spark. Waste does fire twice as often (frequency) as a traditional ignition system, but that doesn't affect WHEN it fires as far as the timing curve goes.
 
Check your needle jet, They have a tendency to oval out. I needed a magnify glass to see it! It made a difference.
What does a plug reading show?
Is it hard to kick when you try to start it? Check your auto decomp on the cam, maybe the spring unwound as is a tendency with this device.
I have a PHM 40 on mine and still have an inconsistant idle and a slight pop on decel. I am interested in what you find out!
Click to expand...

I figured at some point I would just replace the needle jet, but that still doesn't explain why it won't idle yet seems to run fine and have lots of power in higher throttle positions.

The spark plug usually looks a bit more on the lean side, but I haven't run the bike for a long enough period to get an accurate sample in my opinion. Definintely no fouling going on.

This is honestly the only bike I've ever had to kick over, so I don't have a good comparison, but other people have kicked it over and they say it seems normally for a 600 single. The previous owner claims he added auto-decomp, but it still has the lever attached. When I pull the lever, I don't hear any release of pressure (do your hear the manual decomp valve when activated?). I just kick it to the point where I feel the compression building, and then give it on more little push and it clicks. Seems pretty easy to kick over at that point
 
Came across this awhile ago, thought it might help.[attachment=0:xkppfjdv]timing.pdf[/attachment:xkppfjdv]
 

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Hi

schultzy said:
Came across this awhile ago, thought it might help.[attachment=0:1mske1nx]timing.pdf[/attachment:1mske1nx]
Click to expand...

I have wrote this a couple of years ago, it was the best I could find at the time, based on my experience and the fidings of a spanish guy I don't remenber.

I think this can be a good starting point to a initial set up, but you should go after to the strobe light, the sweedish guys aren't very great in the art of making ignitions, so they are all a bit diferent ones from another.

Since here your stator is in the engine you have to do things a bit different than the newer bikes, you have to make your marks, a refernce mark and a tdc mark, and go for the light, having to take out the flywheel each time you whant to make a change.

If you go for it let me know the way you did it.

:cheers:
ZAGA
 
With the strobe light, what mark is supposed to line up at what rpm? I have heard things like holding the engine at a certain rpm to line up the newly made 33* BTDC, but I wasn't sure if this was the same for the older husabergs.
 
Hi

In this ignition you have to make your own marks.
The two lines will have to be align when you put on the strobe light 6 deg. at idle speed (normal one).

:cheers:
ZAGA
 
lee30bmw said:
By the way, does anyone have an ignition timing write-up for the older husabergs like mine? I'm a little confused by the one on the wikidoc. It doesn't mention anything about using locating pin to line up the flywheel to the stator like my manual does. I figured this was because alot of the information of the wikidoc only applies to the 'newer' husabergs.

My stator cover doesn't have a timing plug that I can remove. I pressume you can you run the engine with the stator cover removed instead. Also, I can't wrap my head around why you need to set the gun to 72 degrees instead of 36 degrees becaues of waste spark. Waste does fire twice as often (frequency) as a traditional ignition system, but that doesn't affect WHEN it fires as far as the timing curve goes.
Click to expand...

Hello lee30bmw,
why do you need to halve the advance? Because it is a wasted spark system! Most timing lights are designed for four-stroke engines. The only input they have to calculate engine speed is the frequency of the ignition pulses. As a wasted spark system gives one spark every revolution, the displayed speed on the timing light will be twice the real value unless you have a special setting for wasted spark or two-stroke.

Now, to get from engine speed to ignition advance the timing light simply divides the TIME interval between incoming ignition trigger pulses into 720°, then associates 1/720th of the interval time to 1° of advance. Unless the timing light has any way of knowing it has a spark every 360°, not every 720°, the result is a factor of two error in real advance.

Hopefully that makes sense!

Now if you've got your head around that and you're sitting comfortably, consider what happens if the engine speed is not constant between incoming ignition pulses. Yes? OK, now is the engine speed constant during a complete cycle? :-k

If you've got a good grasp of this, you'll appreciate the use of a timing light is at best approximate. Super convenient yes, but I wouldn't worry if it were a few degrees out either way.

Fun, fun, fun...

Cheers and regards... Paul
 
Maybe the timing lights we are using are different in how they measure timing. I am still confused.

Regardless of whether the ignition system fires one or twice per two revolutions, it should still fire at the same timing with reference to the piston position given a constant engine speed (timing is altered via the ignition module throughout the rev range.)

Maybe a better way to put it is this: lets say you have a single cylinder engine without waste spark. You have your two ignition marks, the moving one and the steady one. Lets say you could spin the engine at a very slow speed. You hook up your timing light, and see that for every two revolutions and around the time of the power stroke, the timing light flashes and the marks are line up to confirm your ignition timing is correct.

Now, you have the same single cylinder engine with waste spark. With the timing light installed, you now see the strobe light flashes when the marks line up. Instead, it does it every time the engine makes one revolution. Being that the ignition module is 'trained' to fire the spark at a given time based of piston (or flywheel) position regardless of compression or exhaust stroke, it shouldn't change the ignition timing, but instead just the number of ignition firing events (doubled).

As far as measuring engine speed with an inductive pickup, I can see how that would be doubled being that timing lights are calibrated to show that every ignition fire is actually two revolutions.
 
Lee,
please read my post again.

As further explanation, consider this: there are two approaches to checking your timing with a strobe light depending on which type you have. Either you have a "static strobe" which gives a pulse at the time of the ignition input, or you have a "dynamic" or "adjustable" strobe with which you can offset the ignition pulse by an adjustable 'angle' relative to TDC. With this second type of strobe, when you set the offset to zero, it behaves in exactly the same way as the first, static type.

Traditionally with the static type of strobe, you make a fixed mark on the crankcase and directly opposing marks on the flywheel with the engine set firstly to TDC and then to an angle before TDC at which point you intend the ignition to fire. When you run your engine at the test speed (idle?), the crankcase mark should correspond with your advanced flywheel mark if your ignition is set correctly. If it is not, you adjust the timing in the appropriate way before retesting, and continue in this way until you're happy, bored or have lost the will to live...

With the dynamic strobe type, you need only set the engine to TDC and make one line on the crankcase and one opposing mark on the flywheel. When you run the engine at the test condition, the marks will of course be misaligned by the amount which corresponds to the ignition advance at the engine speed and load point you're using. You then use the advance control on the timing light to make the marks re-align and the number displayed on the strobe light represents the TIME offset needed between the ignition pulse and the TDC mark to make them appear visulally aligned. As a time offset is not so useful, the strobe converts the time offset into an ANGLE offset... your ignition timing advance figure... based on the current engine speed, which it calculates from the frequency of the incoming ignition pulses. Unless advised otherwise (and if it has the facility for this), the strobe will assume the angle between subsequent ignition pulses is 720°. IF we stuff ignition pulses into it at twice the frequency it expects (the situation with a wasted spark four-stroke or a two-stroke engine), the speed displayed by the strobe will be twice that expected. Which I think you agree with, based on your comment. Now, as the angle offset calculation is based on the engine speed calculation, does it not follow that the angle displayed on the strobe is also doubled?

The absolute key point to understanding this is to accept the strobe light has no idea of the angular position of the engine. It measures the time between ignition pulses and nothing else.

I hope that make a little more sense. If not please ask again and I'll try to re-phrase, or draw a picture.

Enjoy.

Cheers... Paul
 
Ok, that makes sense now. You gotta understand that the two ways I've heard to check ignition timing for these bikes both involve a TDC mark and an advanced mark therefore not requiring the use of an adjustable timing light. If using the self-made advanced mark to set timing with a static gun, I think it should be made clear that you should NOT double the value of the ignition advance. Even the husaberg wikidoc has you go through all the trouble of making a new TDC mark on the flywheel, then making a degree meter, scribing an advanced mark, etc. I guess that's all fine and dandy if you only have a static timing light...

I actually happen to have an adjustable timing light, but I never have used it's adjustable feature as there's really never any need to with most cars coming with the correct markings on them.

With that being said, what are the specs for my bike (98 FE600). I've read between 33-36 at an above-idle rpm, or 6-8 BTDC at idle (1000rpm). Do any of these sound right?
 
Hi Lee,
I'm pleased I managed to explain. Almost immediately after I submitted my last post it became obvious to me you had a static strobe (or were using your strobe "statically")... I simply didn't think this would be the case as I've not seen such lamps for years now. My mistake. Sorry. If I'd spotted this earlier I would have been able to sort you out in fewer words!!!

The figures you quote for ignition timing look about right. There are many items in the "doc" that contradict, but the general consensus seems to be 6 to 8°BTDC at idle (but what speed? 1000rpm sounds too slow) and full advance around 35°BTDC at substantially above idle (speed???). There're a few variations on this theme depending on which engine you have, but that seems to be the best answer I can find.

I've been playing around with ignition solutions for a while on my FE400e and it's clear to me there's much that can be done to improve over the original OEM solution. Unfortunately I'm yet to fully explore significantly higher ignition advances or anything other than a very conservative, linear advance curve. Work to be done...

You mention that most cars come with the correct markings. When was the last time you checked the igntion timing on a car, or do you work with old stuff? I've had the same timing light now for close on 20years, and I think I've only used it in anger ten times. Always on old bikes, never cars; it's just not necessary, and in a lot of cases it's just not possible to get access to the high-voltage ignition cable or the flywheel!

Cheers and regards... Paul
 

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