Question For Lineaweaver; Re:Jetting

Splat · Jun 10, 2004

In the thread about the FCR carbs, you mentioned that you can properly jet carbs on a flow bench without the bike; certains models only of course. I realize that you have a database of conditions and parameters from years of experience. But what need or benefit is the flow bench in the process? Do not two samples of the same model carb flow the same and the jets meter the fuel the same? Or do they vary enough that you need to actually monitor their performance on the bench and fine tune them? Just curious, since you mentioned that mail order jetting was a bad idea.

LINEAWEAVER · Jun 11, 2004

Hi Splat,
If primary variables are known (including displacement and engine state of tune) I can draw from a personal dynamometer / flow bench cross reference data base.

The Dellorto is a primitive carburetor and despite like units can have vastly different flow characteristics.

Under controlled main venturi air flow and / or inlet vacuum I simply measure the signal strength (slack tube water manometer) of the orifice in question.

with exception of the slide and a few other components I rarely use OEM Dellorto hard parts. Quite often I make the metering rods from brass stock and use keihin jets via an adaptor.

FYI:
Albeit far less critical you may be interested to learn that the same rules apply to remote suspension tuning. One may take several identical damper units (front or rear) and find the curves to be quite different when run on a dynamometer.

Hope this has answered your question.

Kind Regards,
Dale

Splat · Jun 11, 2004

I can understand the reasoning to make custom needles, but why use Keihin jets with an adapter, why not o.e.m. Dellorto jets?

So, a person is faced with the option of spending $150 to have the Dellorto properly tuned versus $550 for an FCR conversion.

Will the Dellorto perform as well as the FCR? Or, since it is a primitive design, will the Dellorto always be second best to the FCR?

I presume these are common questions on the minds of several members. Since the FCR topic seemed to run around in circles on this issue.

I think everyone really wants definitive answers regarding "What do I get for the $150 tuning?" and "Is the FCR really worth $550?"

Is it possible to answer those questions in torque and horsepower values/ numbers?

With regards to the suspension issue, ****'s Racing machines his own internal valving components to achieve his desired results. I very happy with the improvements that he made on my suspension.

LINEAWEAVER · Jun 11, 2004

Splat said:
I can understand the reasoning to make custom needles, but why use Keihin jets with an adapter, why not o.e.m. Dellorto jets?

Wrong (for the particular circumstances) flow coefficient and large deviation among like sizes.

So, a person is faced with the option of spending $150 to have the Dellorto properly tuned versus $550 for an FCR conversion.

Many options exist including that of using a Mikuni.

Will the Dellorto perform as well as the FCR? Or, since it is a primitive design, will the Dellorto always be second best to the FCR?

Depends upon ones objective. Example: Peak power / brite throttle repsponse vs soft / linear power delivery.

I presume these are common questions on the minds of several members. Since the FCR topic seemed to run around in circles on this issue.

I think everyone really wants definitive answers regarding "What do I get for the $150 tuning?" and "Is the FCR really worth $550?"

I have done only two mail order Dellorto carburetors. Both as favors to desperate UHE site members. With rare exception Dellorto modifications are simply a part of what I do when building and / or tuning a Husaberg. It is not a stand alone generic service.

Is it possible to answer those questions in torque and horsepower values/ numbers?

All else remaining equal and for a given size the FCR will move more air and consequently provide for more peak horsepower.

With regards to the suspension issue, ****'s Racing machines his own internal valving components to achieve his desired results. I very happy with the improvements that he made on my suspension.

Unlike a definitvely rich or lean air / fuel ratio suspension tuning is subjective. Within reason and regarding suspension settings "what one has deemed horrible may be hailed as perfect by another".

.

Sincerely,
Dale

Splat · Jun 11, 2004

LINEAWEAVER said:
Unlike a definitvely rich or lean air / fuel ratio suspension tuning is subjective. Within reason and regarding suspension settings "what one has deemed horrible may be hailed as perfect by another".

Sincerely,
Dale

I don't think there is anything more subjective than suspension tuning.
One man's 'plush' is another man's 'mush'

Thanks for all the replies.

HUSABOMBER · Jun 12, 2004

I have to tell you Splat, when Dale rebuilt my Dellorto on my 400, the difference was staggering.

I really had no problem close to sea level. But when I took the bike a few thousand feet up, it would hesitate, die, sputter, you name it. Excessively rich condition.

I am no carb expert, And I cannot say from first hand experience how the Keihin would compare. But I was well pleased with the work performed.
Throttle response was crisp and linear.

Hope this helps,

John.

Splat · Jun 13, 2004

As Dale stated, he does not offer it as a stand alone service.

As long as my engine stays together, I won't have need to send it to him for any service.

I've built and rebuilt racing engines. I'm in the middle of a CRF project for my son at this time.Short of blueprinting, I am capable of any mechanical work needed to keep an engine running.

My shop currently lacks a mill and lathe, but I have been considering adding them to it.
Then I will be able to perform my own blueprinting, machining and custom fab work.

radiomankev · Jun 14, 2004

I just bought a new "Old style FCR" (no choke/hot start) and am currently testing it. Out of the box it showed no INCREASE in performance. However, the bike seemed to vibrate a little less and run cleanly. 170 main, 48 pilot, 200paj, ocems (?) on clip #4.-2000 FC501. I have moved clip to #5 (from bottom) and the leaner needle setting has livened it up. I am going to try 165 main today.

One interesting observation: When I slid out on a turn on the MX track (Hangtown) and dumped the bike, it just sat there running like a little kitten! ON ITS SIDE! The dellorto would die as soon as it went over--even if you grabbed the throttle.

I'll report more results later.

Question For Lineaweaver; Re:Jetting

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