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Do I need a hot start?

Bergini

Bergini

Joined May 2011
700 Posts | 3+
Wisconsin, U.S.
Have a funny scenario happening lately, just rebuilt this old hotrod and installed a mikuni phm 40 pumper carb and a ton of other mods which could be throwing something off......spes exhaust, high comp piston, pod filter, taffy sledge, mototuneusa ported heads, '08' camshaft,

Cant kick start the bike cold but starts within 1-2 seconds of cranking of the button and needs choke.....

Can't start it on the button when hot, but will kick start 1st kick hot eveytime w/o choke......

when i do try the e-start when hot the bike does the following when i press and hold the button for five seconds:

crank crank crank pop crank crank crank pop crank crank crank pop....I flip out the old kicker and jump on it once and i am off.

this stator is used but taken off a bike many years ago and looks new, tests good, and increase the performance from my original but still working stator. carb is nicely tuned with an accurate wideband a/f ratio guage like used in dynomometers...........since the rebuild this has been how it is it hasnt gotten better or worse.....after the engine build but before the 08 cam, i had the 55 cam and the rest of the setup was the same and it would kickstart easy cold but the battery was dead and wouldnt e-start at all with the high comp piston unless it was on a battery charger, then it would pop off with e-start hot or cold....all of this experimenting has taken place within about 6 hours of engine running time.

Any thoughts ancient husagods? :cheers:
 
ancient husagods?
Click to expand...
?? really :roll:
i'd guess your stock stator is dying, breaking down when hot. but you have muddied the waters with all the mods. try to solve the problems one at a time.
the phm is the round slide? try to experiment with the pilot jet. what is your jetting?
 
oh crap, the carb on it now is a mikuni tm40 not the dellorto

actuall it got it started fine this morning cold kickstart, not sure whats up, ill figure it out, lol as long as it starts somehow i dont care haha
 
My bike has a hot start, but I never use it. I do pull the manual decomp though if I dump it on the trail. I let it spin a few times then release it and it fires right up.
 
Yea all bikes are different on that matter from what i have read, two exact bikes side by side one will need the hot start the other one wont....also mine doesnt have the manual decomp only the auto..

I havent done a lot of riding yet sinces its been assembled, i think its got 150km on the meter. its been rainy and stuff and im waiting for my last jet order to show, hopefully tomorrow, i got a different needle to try and a smaller main....nothing that will affect the idle/start circuit though....

realized last time i rode that my battery has slowly been getting sucked down to nothing and after a quick inspection i find it not charging at all, havent looked at it since since its been raining and cold again. likely knocked a wire off when i put the tank on....

Ill do a little more experimenting and post back,
 
Maybe let me ask this question:

For guys who have a hot start and seem to need to use it for hot e-starting, what happens if you dont use it?
 
Bergini said:
Maybe let me ask this question:

For guys who have a hot start and seem to need to use it for hot e-starting, what happens if you dont use it?
Click to expand...

It won't start. Usually when warm, I pull the decomp, hit the starter, and as soon as it turns over let out the decomp and it starts right up.

When hot, I do the same and it cranks 4 or 5 turns without starting so I let off the starter. Try this 3 or 4 times and the cranking is getting weaker.... Hey, duh, try the hot start. Then it starts right up.
 
hhhm, i do not have a maual decomp to pull but that does make me think, you guys who have the manual decomp can release more pressure and spin it faster by pulling it so it clears out the cylinder of fumes and stuff better thus helping it to start a little leaner/easier when hot, which is also what a hot start does.....i havent played around with it enough yet to actually go and modify it for a hot start but ill get it figured out, my jets just showed up today so experimenting will start soon..... :lol:
 
interesting find last night, the charging problem....

originally the voltage rectifier was bolted to the plastic rear upper flap or upper inner fender, during the supermoto conversion I made my own aluminum upper inner fender/flap and used an acerbis lower universal plastic mud flap and had the voltage rectifier in the original location....bolted to the upper flap......which now was grounding to the subframe and preventing it from charging (yea i know right :lol: ), basically i just unbolted it and put a dummy bolt/nut to hold the secondary wire against it and wrapped it in tape and left it under the seat tucked in with the rest of the wiring.....glad i went right for that 'just to be sure' as it was the only thing i modified and the wires that i though had probably came disconnected when installing the tank were still connected......

with the charging problem fixed and battery recharged/recharging it seemed to be starting on the button hot or cold everytime today, i did give it a quarter turn out on the idle screw (which should have richened idle but it seemed it wasnt dropping to low idle when hot and maybe was the whole problem) and i did change some mid-wot jetting but that shouldnt have affected it.

maybe it just wasnt spinning it over quite as fast in the begining and obviously thte charging thing has been there since i did everything, remember this thing is totally modified and in the begining stages of road testing/tuning :D
 
Ok so maybe i got a two for one deal with the charging system thing i dont know, today with engine hot or cold starts on the button like nothing ever happened and i ran lots of little starting and stopping errands today probably 8-10 hot restarts....all is fine, started immediatly when pushing the button, i am confused as to why but do not really care since its starting as designed now, wish i knew for sure what fixed it but ill probably never know.......
 
Just to add info for anyone in the future who might do a search on "hot start":

What the hot start does is open a passage in the carb to add air to the mixture which, under the conditions of a stall during a race, has probably gone very rich causing the engine to be difficult to restart. Well, on the old engines (pre 2000 depending on model - let's call them Gen 1), there is a vacuum port machined into the area of the cylinder head where the carb boot bolts on. This port provides a vacuum signal to the fuel pump that pumps fuel from the low side of the fuel tank up to the area where the petcock is. This pump works whenever the engine is running (and maybe even a little bit when the engine is being started) and any excess fuel getting to that area of the tank just spills back over to the low side (right side) of the tank. Now, when the pumper carbs first started coming out, it was quickly determined that a way of activating the hot start from the handlebars was needed and one of the early designs involved a tube running from the carb hot start circuit to a valve on the handlebars. I found one of these hot start relocator kits on ebay and mounted it up because I'm running a Keihin pumper carb from a Honda TRX 450 that didn't have a hot start circuit. Thusly I have the tube leading from the handlebar valve to the vacuum port on the intake. It works great. Mind you, my Gen 1 engine (with the vacuum port) is mounted in a 2003 frame which doesn't have part of the fuel tank located below the carb and doesn't need the fuel pump. I suppose the same setup could be used on the Gen 1 bikes that need a hot start and you would just "T" into the hose going from the vacuum port to the fuel pump and hope that the extra air volume won't affect the operation of the fuel pump.

It sounds like Bergini has his issues figured out but, in case someone needs to reference this thread and actually needs a hot start...here ya go.
 
hhhhm, i actauly still have my issue to some extent, seems the longer the drive the more likely it is to not start on the button and needs a kick start......to some extent opening the throttle slightly before i hit the button does help.......i switched my fe tank to the fc tank and no longer have the fuel pump either.....i am going to try putting the intake pulse tube hole to use....thanks for the advice thorgan, i forgot i plugged that hole off when i convertered to the different tank.......up till today opening the throttle had seemed to be helping and it only didnt e-start once and i used it three times or so....
 

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