Timing Issue

1959 - 1978, M151, M151A1, M151A2, Technical questions and discussions, regarding anything related to the M151.
CaptB
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Re: Timing Issue

Post by CaptB » Tue Mar 30, 2021 9:38 pm

Thank's Rick, I will figure out when the back fire is happening and check the exhaust joints. How do I fix the accelerator pump. Never had the carb apart it is NOS


Rickf
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Re: Timing Issue

Post by Rickf » Wed Mar 31, 2021 4:42 am

When you tell me it is an NOS carb that kind of makes things tricky. The problem with these carbs is they have a vacuum operated accelerator pump so you have two systems involved in making the pump work. You need the vacuum system to be working correctly and you need the gasoline system to be clear and working. Usually when I see this complaint it is with an older carb and the problem is usually a bad diaphragm in the pump. When you say it is a NOS carb that can mean several things, It is new old stock from Zenith and only a few years old, it is new old stock from a surplus dealer and can be 40-50 years old, or it could be a cleaned up carb that someone passed off as NOS. What are the numbers on top of the carb? Should be something like 13660, 12848. The 13660 can have an A or B after it. How long have you had the carb? And what gas are you using?

I just realized you are in Greece so the last question about what gas probably will not help me as I am not familiar with the gas ratings there but if you are running a premium gas try running regular gas instead. Premium is designed to prevent preignition and is less volatile than regular and will not run as well in low compression engines.

You can try taking the intake hose off between the carb and the air cleaner and run the engine. NOW, Be aware that what I am suggesting could produce a backfire from the carb back at your face so wear eye protection and be prepared to lose a few eyebrows and some hair if it happens! It will be running lean without the intake hose. That said, With it running and looking into the carb mouth from a safe distance give it some gas and see if there is a substantial addition of gas added from the center tube. Try lightly accelerating it at first and then harder each time. It will not backfire until you hit it really hard and it may not then but I need to warn you just in case. If it is not pushing a substantial addition of gas as soon as you hit the throttle then you have a pump issue. Last test is when you shut it off. Leave it idling at normal speed and just shut it off like normal with the hose still off, you should see some gas run out of the mouth of the carb. If this happens then the pump IS working correctly. It pumps out the last load of gas in the chamber as the vacuum dies off when the engine is shut down. If this is the case we will need to look at mixture, you can readjust your mixture and when you have the best idle then back out the mixture screw 1/4 turn at a time and see if that fixes it. If it does then you may have dirt clogging the passages and you will need to take the carb apart.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

CaptB
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Re: Timing Issue

Post by CaptB » Wed Mar 31, 2021 6:57 am

Thank's again Rick, I will go through this in the next few days and post the results

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W. Winget
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Re: Timing Issue

Post by W. Winget » Wed Mar 31, 2021 9:04 am

Rick:
In 5 out of 7 Carbs I disassembled from "service" released engines (i.e. no bubba's, just "trained" :oops: mechanics) the accelerator diaphragm and spring were installed backwards.
Guess the TM was not too clear in the illustration on it.
V/R W Winget
Looking for 1918 Standard B 'Liberty' truck parts

Rickf
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Re: Timing Issue

Post by Rickf » Wed Mar 31, 2021 9:57 am

I have also seen that many times but in that case the engine just falls completely flat and dies. If his only has a little flat spot on acceleration I suspect dirt.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

CaptB
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Posts: 28
Joined: Sun Mar 14, 2021 10:01 am
Location: Greece

Re: Timing Issue

Post by CaptB » Wed May 05, 2021 9:23 am

Hi Rick, first off I don't know what happened but my last reply didn't post. Ok found the exhaust leak now fixed. The nos carb is a reproduction I found on e bay and when I fitted it it ran great all that summer. It may need looking at but I am going to strip down my original and fit that. I have a few questions but I am going to start a new post as the timing is now fixed.

Rickf
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Re: Timing Issue

Post by Rickf » Wed May 05, 2021 5:22 pm

Ok, I replied to your post but you say it is a 13660? What numbers are on top of the carb? 13660 or one single string of numbers? Either way it is a 13660.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone


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