Carburettor question

powerwagontim · Post by **powerwagontim** » Sun Jun 05, 2011 5:10 am

I got my truck running for the first time this weekend, a rebuilt engine, rebuilt card etc. It runs well, but only if the choke is pulled out about 3/4 of an inch. That tells me vacuum leak, so I double checked and do not find one. I sprayed ether around the carb, and didnt get any increase in revs. I played with the mixture screw but I couldnt make much difference with it. What would the next step be?
Thanks,
Tim

ZGjethro · Post by **ZGjethro** » Sun Jun 05, 2011 8:48 am

Are the problems all the time, higher revs, or off idle? If it is in the higher revs, a larger main jet might help if you are running lean. You could check for blockages in the low speed circuits also. Hopefully some more experienced wrenchers will give their input. I barely know the basics.

cuz · Post by **cuz** » Sun Jun 05, 2011 9:09 am

The need to leave the choke out to keep her running can be two different avenues of troubleshooting. 1-Too much air. 2-Not enough gas.

With the choke pulled out to help it idle ok what effect then does the idle mixture screw have?

As asked above, Do you still need the choke out when operating above idle?

M37UK · Post by **M37UK** » Sun Jun 05, 2011 1:32 pm

Could it be as simple as the choke cable needs adjusting at the carb?

powerwagontim · Post by **powerwagontim** » Sun Jun 05, 2011 2:48 pm

Hi Cuz,
with the choke pulled out 3/4 of an inch, I dont get much change with the idle mixture screw. I began with an initial setting of 1 turn out, I can turn it just about all the way in before it dies. Turning it out further does not seem to change it much.
I didnt think to try pushing the choke in while driving it, I suspect it would stay running until I put the clutch in and let it go back to idle.
When you say not enough fuel, are you thinking fuel pump or float setting, or more internally within the carb? The float is set 1/8" below the bowl.

Stu,
The cable is adjusted fine, closes the butterfly when pulled, opens the butterfly when pushed!

Jethro,
I had the carb apart and put in a new kit. I blew carb cleaner through every hole, from both directions, got good spray through each. The jet is the one it came with, it should be fine.
Thank Guys,
Tim

MSeriesRebuild · Post by **MSeriesRebuild** » Sun Jun 05, 2011 4:48 pm

You mentioned your float setting is 1/8" below the top of the bowl. That is incorrect, typically it should be no lower than 5/64" below the top edge when the needle closes off the fuel flow.

powerwagontim · Post by **powerwagontim** » Sun Jun 05, 2011 5:13 pm

Hi Charles,
I spoke with a man at Daytona parts, who specialize in carb rebuilding. He also said that the setting is 5/64" but also added that with todays gas, they add from 1/32" to 1/16" inch to the 5/64". 5/64" plus 3/64" (between 1/32 and 1/16 ) equals 1/8"
That is how I came to set it at 1/8"
Tim

MSeriesRebuild · Post by **MSeriesRebuild** » Mon Jun 06, 2011 4:07 am

powerwagontim wrote:Hi Charles,
I spoke with a man at Daytona parts, who specialize in carb rebuilding. He also said that the setting is 5/64" but also added that with todays gas, they add from 1/32" to 1/16" inch to the 5/64". 5/64" plus 3/64" (between 1/32 and 1/16 ) equals 1/8"
That is how I came to set it at 1/8"
Tim

I understand, but with today's gas being obviously very different as you travel to different areas of the country. There is no good default setting that will work perfect for everyone any more. 5/64" still works well for us in most carbs, but in some other area where gas may be significantly different, you may have to do something different in order to achieve the best set up. I always suggest starting out at 5/64", then adjust from there if needed. You'll have to work at it to see what is best with your available gas blend.

vargaspj · Post by **vargaspj** » Thu Jun 09, 2011 10:11 am

Charles, if his float is set lower than spec wouldn't it be closing the needle on the seat with the fuel level in the bowl at a level lower than normal and possibly be causing him to run too lean at idle? Cutting out the airflow with the choke would then richen out the idle mixture (less air) and possibly allow it to idle. Sounds like the first step would be to reset the float level. I know a long time ago when I took a carb rebuild course at my local JC that this was one of the first things set when we put them back together and it was really stressed that if you didn't get it right it could cause you all sorts of trouble when it was fully assembled.

MSeriesRebuild · Post by **MSeriesRebuild** » Thu Jun 09, 2011 11:08 am

vargaspj wrote:Charles, if his float is set lower than spec wouldn't it be closing the needle on the seat with the fuel level in the bowl at a level lower than normal and possibly be causing him to run too lean at idle? Cutting out the airflow with the choke would then richen out the idle mixture (less air) and possibly allow it to idle. Sounds like the first step would be to reset the float level. I know a long time ago when I took a carb rebuild course at my local JC that this was one of the first things set when we put them back together and it was really stressed that if you didn't get it right it could cause you all sorts of trouble when it was fully assembled.

Any # of possibilities certainly could exist, however if the scenario you suggest were to be his issue, then the float height should be set so that all comes together at the happy medium without the necessity of running with the choke partially on.

M37UK · Post by **M37UK** » Thu Jun 09, 2011 11:19 am

You have got me wondering about my float level now, as I run with choke out a bit also.

Is it easy enough to make a gauge to check this or do you jmust adjust it using a ruler or something?

Cheers

cuz · Post by **cuz** » Thu Jun 09, 2011 8:31 pm

Generally speaking a minor lowering of the float level (thus the fuel level in the bowl) will not have a very noticable affect on idle mixture. The idle circuit can usually accommodate a slight flux in bowl fuel level but it will not tolerate restrictions in it's passageways, air leaks or damaged mixture screw tips and seats. A more common source of lean idle issues is a bad main body gasket that doesn't seal the top of the low speed passageway. Note the extra steps required when using a spring loaded float needle.

Here's a few helpful photos:

: ETW1 Notes.JPG (126.84 KiB) Viewed 3516 times

: carb1.jpg (164.89 KiB) Viewed 3516 times

: carb2.jpg (186.81 KiB) Viewed 3516 times

cuz · Post by **cuz** » Thu Jun 09, 2011 9:38 pm

Here's a couple of TM 9-1826A pages that may help:

: 150 CH 12 B&B w-Gov.JPG (247.83 KiB) Viewed 3516 times

: 154.jpg (226.41 KiB) Viewed 3516 times

powerwagontim · Post by **powerwagontim** » Sun Jun 12, 2011 2:36 pm

When I was playing with the carb last week, the air horn was removed. I put it on today, with the air cleaner (no oil in the air cleaner yet) and I was able to get it to idle without any choke. Perhaps the amount of restriction given by the air cleaner and air horn was enough to allow the choke to be opened fully?
Tim

Post by **Cal_Gary** » Sun Jun 12, 2011 7:54 pm

Call my carb finicky, but my float has to be EXACTLY 5/64th or I have difficulty--must have popped that top 4 or 5 times to get it just right (not too much fuel nor too little).
Gary

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