TOPIC:

Hey guys, I just went through my set of carbs and made sure nothing was clogged and everything was clean...set float levels and then installed them on the bike.
Here's the problem...while syncing the carbs I was able to get 1,2 and 3 to sync up nice but was getting no readings on 4. I checked my hoses and even swapped one to make sure it wasn't the Carbtune. I also noticed that I get little if any response by turning the pilot mixture screw. There is a sweet spot near almost closed that the #4 carb is trying run properly. the other 3 run great but it sounds like it's only running on 3 1/2 cylinders.

What did I do?????

Could there be an air leak somewhere on # 4 causing no or weak vacuum ? Perhaps not sitting properly on the #4 intake manifold.

Is the #4 exhaust pipe getting hot - spray water test ? Is the #4 spark plug wet with gas or dry ?

Just some ramblings on my part.

Thanks JR, I will check that.

cnyl wrote:

...set float levels and then installed them on the bike...while syncing the carbs I was able to get 1,2 and 3 to sync up nice but was getting no readings on 4...get little if any response by turning the pilot mixture screw. There is a sweet spot near almost closed that the #4 carb is trying run properly...

Excellent suggestions from JR.


Might next check actual float level of #4 carb while on the bike and motor turned off (the clear plastic tube method). Assuming the pilot mixture screw richens when screwing in -- might possibly indicate a too low float level Just guessing a little, but don't fully trust bench-set float levels. Also wondering if the pilot jet on #4 might possibly need additional cleaning if not allowing enough fuel to pass.

Patton wrote:

Might next check actual float level of #4 carb while on the bike and motor turned off (the clear plastic tube method). Assuming the pilot mixture screw richens when screwing in -- might possibly indicate a too low float level Just guessing a little, but don't fully trust bench-set float levels. Also wondering if the pilot jet on #4 might possibly need additional cleaning if not allowing enough fuel to pass.

I'll check the level while on the bike. It may be set to high. A little droplit of gas was on the drain spout and looked like it was leaking.The pilot mixture screw has no effect except for a slight jitter:blink: in idle near closed. The jet is super clean.
Would to much gas cause this?
I checked as JR said and have no leaks. I still can't figure out why it has very little/no vacume at the nipple on the boot.

When I try to sych #4 to match the other 3, it effects the vac levels for 1, 2 and 3 but not it's own. It doesn't even move the bar on the carbtune.

Post edited by: cnyl, at: 2006/12/31 23:58

Post edited by: cnyl, at: 2007/01/01 00:05

The #4 carb has a port for the Vacuum petcock. Make sure to plug it. In order to sync the carbs you have the tank off right? That means the vacuum tube needs to be plugged.

JR wrote:

...Is the #4 exhaust pipe getting hot - spray water test ? Is the #4 spark plug wet with gas or dry ?

What were results of spray water sizzle test and appearance of plug?

If not already done, would suggest first eliminating possible non-carb problems with #4 cylinder before focusing on the carb. Recommend compression test, and if low, check valve clearances and adjust as needed. Check spark on #4 plug (could be faulty plug, wire and/or cap). Assuming ignition timing okay because other cylinders seem to be firing all right. Conditions in #4 cylinder may help explain lack of vacuum at boot nipple. As I understand it, suction from the cylinder (properly seating valves and compression) pulls fuel mixture through the carb (over-simplified version).

Assuming good compression and good spark and proper timing, then back to focus on incoming fuel mixture.

Fuel leakage from drain spout may result from an improperly seating float needle (crud or wear) or float level set too high whereby the flat tab fails to push the needle completely closed against the seat. But this would seem to produce a too rich condition which seems inconsistent with better running at the richest pilot air screw adjustment (screwed almost all the way in)-- so no answer yet for that phenomenon.

Don't know why attempted sync of #4 is affecting vac levels on the other carbs while having no effect at all on #4. Thought each carb-cylinder combo was independent from the others, and synched to get each carb function as close as possible to the others so that all cylinders were pulling equal duty (another over-simplified version).

Just trying to help, and could be mistaken about some of this, but do know it's best to cover all the other performance bases first before wading into carb work.

BTW, how was the bike running before any of the carb work was done?

Looking forward to seeing you up and running strong on all four.

Post edited by: Patton, at: 2007/01/01 03:22

delete duplicate post

Post edited by: Patton, at: 2007/01/01 03:19

Thanks Patton, i'll be checking all today. It ran good before I did the carbs. I do not have any vac lines plugged. I will make shure to do that. Thanks for all the typing...

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loudhvx wrote

The #4 carb has a port for the Vacuum petcock. Make sure to plug it. In order to sync the carbs you have the tank off right? That means the vacuum tube needs to be plugged

cnyl wrote

It ran good before I did the carbs. I do not have any vac lines pluged...will do that

Seems this could account for lack of vacuum at the #4 boot nipple. Anxious to hear the results from following the above -- hope it's works like magic.

If not already using an in-line fuel filter, would recommend doing so, and also cleaning the petcock filter (if applicable). And while the tank is off, rinsing it out well with fresh gas. An easy gas disposal method is to leave it outside in a wide container (disposable turkey baster?) to just evaporate.

Post edited by: Patton, at: 2007/01/01 13:27

Post edited by: Patton, at: 2007/01/01 13:28

cnyl wrote:

Thanks Patton, i'll be checking all today. It ran good before I did the carbs. I do not have any vac lines plugged. I will make shure to do that. Thanks for all the typing...

The petcock should have two hoses to it.
The small one needs to be plugged for carb syncing. Also, make sure the hose is not cracked and the petcock is not leaking, otherwise it will run bad when hooked up.
It goes to the #4 carb and is full manifold vacuum. It opens the petcock when the bike is running.

Here's a picture of the port on the #4 carb. If the other carbs have this same port, (they usually don't) they should already be capped off.



Post edited by: loudhvx, at: 2007/01/01 16:17