Suspect M135 vacume advance problem

[jollyroger]

You are right. It's not magic.I have been through hundreds of carbs in my life. 1 bbl., 2 bbl., 4 bbl., Variable venturi, 2 singles, 3 singles, 6 singles, 8 singles etc. Mikuni to Rochester to Carter to Weber. Just about every combo of carb.

The basic principles are the same. Once you break it down to systems and sub systems it makes it more logical to deal with. It also compartmentalizes the tasks at hand so you can stay focused on how to diagnose and fix the problem.

 

[Brad]

HEy Guys,
I can't tell you all how much I appreciate your support and help with this problem.
What has me so frustrated is that this is my Dad's truck. Sixty years ago he was at the frozen chosin, and he's 81 now.
He's still ok but not near what he was last year. We been on this truck for three years now and he only had one ride.
I just want him to be able to spend some time in it.
We are not professional mechanics but have alwways done allot of our own work.
I spent most all summer and now fall replacing the engine and changing this thing from automatic to standard at his request cause we had tranny problems and he said this engine was rebuilt about 10 years back and never ran.
The only parts we reused were the distributor and Carb and we have the same running problem.
Although the tranny problem seems fixed.
Thanks again, I really appreciate the help.
Highest regards,
Brad Foust

 

[Oldfart]

Brad,
Let me understand. It sounds like you have changed the engine and used the old distributor and carb on the new engine. Did you have the same problem on the old engine?

Oldfart

 

[Brad]

Yes sir, very similiar, but not near as bad.
A momth oe so ago right after the change we fired it up and it ran pretty decent but with the same little cough or backfire when accerating out of idle.
We thought it was probably a timing issue and a friend with the right equipment was going to set it foe us correctly.
But when driving it it seemed that when going arounf 35 or 40 and trying to accelerate it would also then start cutting out like it didnot like gas.
But now its been getting worse and worse.
But yes its similiar to befire and I assume the same problem.
I am going to set the float here this afternoon.
It that dont help I dodnt know what to do.
Thanks as always
Brad

 

[Oldfart]

Brad,
My son (Jollyroger) and I are sitting here together (working on buying some surplus). We have discussed your issue at some length and this is what we jointly think; First, you need to get the carb set up right so you do not mask other issues. Are you using the stock electric pump in the tank? The reason we ask that question is that some aftermarket electric fuel pumps can have higher pressures that might push the float needle and seat open and flood the carb. Assuming, that is not a problem, then check the needle and seat to make sure they are not sticking and make sure the float moves freely. Set the float per Jollyroger previous post and/or the TM (available in the resources section of Steel Soldiers.) When you get the float system set then post us with the results.

Oldfart

 

[Brad]

Friends,
OK, I set the carb float as directed, while still on the truck. Then turned on the fuel pump (not original) and watched it fill the bowl while still apart. Ran up to about 1/4" to 1/8" from top and the needle valve stopped it like it should.
Then put it all together with the idle valves two full turns out.
Then started it up and had no more gas leaks!!
Was really running rough and the idle valves did nothing.
So I loosened the distributer and by ear turned it until it smoothed out pretty good.
Here is a problem. It seems the wire coming out of the side is really beeing driven into the nblock. In fact, I wthink the distrb needs turned even farther to get the timing just right, but I cant turn it anymore cause the wire is pushed too hard against the block.
I think this is something thats not as it should be?
Anyway, it was running allot better. Then I tried the idle valves again and they did seem to help smooth it out even more.
Then when I would accelerate quickly it had almost quit backfiring thru the carb, but not quit. But a whole lot better and almost drivable.
So I took it for a drive out the road. When about three miles and it seems like its pulling a house, but all in all running ok. Even had it into fifth gear but never over 40 MPH, and very hard to pick up speed. Just seems like a stone sled.
But then on the way back it started cutting out real bad. Barly able to keep it running and get home. Real bad.
Got back here and checked for gas leaks, NONE.
Felt the coil. Not really hot. Just warm like the reast of the engine.
So although it seems better, I still can't count on it.
I looked at the points yesterday and they look fine. I just put them and the condenser in last summer and it's not been ran five hours since.
So friends, what do I do now???
Thanks in advance
Brad

 

[NDT]

The coil on the dist should be clocked completely away from the engine. Sounds like the dist is stabbed wrong.

 

[butch atkins]

carb problems

am looking at TM 9-1826D,ORD. Maint. Carbs,Governors .HOLLEY,the manual for these carbs,what you are saying is not covered in this manual,i think you have more than a carb problem,are the plugs sooty,pull them out and see,there is a fitting in the vent line that is threaded into the gas tank behind the original fuel pump mounting plate,this fitting is spring loaded with asteel ball check valve,it releases excess pressure fro the fuel tank into the vent line system,on my truck i had to take this fitting apart and clean it ,the steel ball had frozen into place and as the truck ran ,gas sloshing around built up excess pressure inthe tank,pushing gas past the float/needle seat/valve assy,and making the truck run really rich,black smoke and sooty plugs,i had rebuilt my carb also and i kept wondering why when i would remove gas cap it would go "whoosh",check valve was frozen closed ,it would take a while driving for the pressure to build up and then truck ran really rich,next time u drive ,check gas cap to see if excess pressure is building up in the tank,hope this helps,keep posting

 

[armytruck63]

I agree with NDT. There is no way the distributor case should hit the side of the engine block when setting the timing. I don't know this distributor, but if it has a gear drive at the end of the shaft, it could be off by several gear teeth. If there is a tang on the end, it could be 180 degrees off.

 

[butch atkins]

carb problems

TM says max fuel pressure should no more than 3lbs,u should check this,also when you rebuilt carb,which hole did u put the pump link lever in ,there are 3 holes and for normal temps the lever should be in the center hole,the other ones are for extreme cold/ hot weather operation,this is the 1st thing the TM says to check for for poor acceleration,next thing is insufficient accelerator pump discharge ,and these are the ONLY 2 things listed in the TM for poor acceleration for these carbs inthe troubleshooting section.TM 9-1826D,

I cant remember who i got to scan all of my manuals for the G-749 GMC trucks to this site but if he will contact me i will see if he will scan this manual to the resources section so that others can have access to this extremely informative manual

 

[G-Force]

Do you have a timing light?
If not go to Sears and buy one. Hook it up and check your timing. Then adjust to spec.
If you can't set it due to distributor hitting block remove the distributor and reinstall it so you can set the timing. You can't diagnose anything unless your timing is set.

 

[Oldfart]

Brad,
I just checked my downloaded copy of the TM on Steel Soldiers. It says that it is possible to install the distributor 180 degrees out of synchronization. The distributor is gear driven with an indexing slot that can allow the distributor to completely seat in one of two positions. At this point, I suspect the distributor was partly installed and then the engine was bumped until the distributor dropped into the slot. Another possibility is that the plug wires are installed in the wrong holes on the cap. It is probably best to download a copy of the ignition section from the TM and follow those procedures to make sure your timing is set up correctly. There are instructions for finding top dead center of number one and then making sure your rotor points to the #1 spark wire. That should put the distributor body in the correct position. Since the ignition system is sealed, you can make a pretty good approximation of proper timing by using a vacuum gage and setting the timing to maximum vacuum.

Oldfart

 

[Mastertech]

yes get your timing set to spec if not a little advanced. remember these engines only have
6.nothing compression ratio so a little extra BTDC aint going to hurt anything.
If you have to bring it up on top dead compression #1 and poke the dist in and wire the cap from there. then set
the timing with a light. see what happens and go from there but also dont forget that after it ran for awile you
might of had a fuel starvation problem causing the dieing and barly making it back home.
I had this happen with a replacement fuel pump on my truck
and remember that just because its new doesnt mean its good
just means you are the first one to test it.
good luck have fun and let us know how it goes.

 

[dragonwagon]

Running smooth once the rpms are up sounds like carb pump to me also .

Does this have a manual choke ? Pull the choke a bit and see if it helps , if so your lookng at a carb issue . jets may be plug some too .

 

[Brad]

THis is great information and I very much appreciate everyones help.
Lots of things to check out.
I will give them a try one at a time and see what happens.
Thanks to all,
Brad

 

[jollyroger]

Good luck and please keep us in the loop. I want to know how it turns out for you.