Etw1 & engine tuning

[GUNNY 155]

Okay guys I could use some opinions. I have the stock Dodge 230 that I rebuilt that is also balanced and blueprinted. I have a bit of a flat spot coming off of idle. I have the timing set at about 7 degrees and hesitate to push it farther. I realized that this would be a given using todays fuels rather than what the engine was originally run on. So first question, what is being run for initial timing by you folks out there. BTW I am using 24v all GI ignition system. The advance curve on the distributor is also factory. What I am thinking is the flat spot is caused by a lean accelerator pump. The carb has been rebuilt so all that is fresh. Now I am an old muscle car guy and have plenty of experience with Holley, Carter AFB's and all the 3 duce set ups from back in the day. All those had mechanical accelerator pumps and could be adjusted as rich or as lean as you needed them to be. I have studied the info for the ETW1 on the M37 and realize that the accelerator pump circuit on this carb is vacuum operated so how well it operates is based on manifold pressure and inches of Hg. It also would be logical to assume that there is no way to adjust the function of the accelerator pump. So my second question is this. Is that flat spot just the nature of this carb? When driving I can sort of feather the gas pedal to get around it but it is somewhat annoying. Besides that my OCD side wants perfection when I have this restoration finished. So looking for any advice you guys can toss my way based of experience of solutions you have found.

 

[tbone1004]

you may want to go to dual carbs. It wasn't a stock option on the M37 but that engine did have a twin carb option. I think 7* might be a bit too far advanced. 4*btdc is considered optimum by the engine builders for these things. What do you have for idle rpm? You may have the idle a bit too fast and it isn't sitting back on the idle jet. When I got mine I was curious why the screw didn't do anything, but then I got a tach on there and realized it was up around 800-900rpm instead of down at 600-650 where it is supposed to be.

 

[rchalmers3]

As a diagnostic you may want to try some external fuel enrichment at the moment of hesitation, to see if your assumption is accurate. I used to use a propane bottle with a hose attached to meter a little additional fuel into the air horn of the carburetor. I think this method is much safer than trying to use liquid or vaporized gasoline. You may need a second soldier to operate the throttle while performing the artificial enrichment.

As you indicate you may already know, getting the acceleration pump shot squared away is not too hard, but sometimes the pump pistons out of the kits are kinda old for the purpose on these old beasts.


My best guess is the fuel delivery is your main culprit, however another idea is to confirm you have steady, sufficient vacuum in transition off idle. There can be numerous reasons for losing vacuum, but if it ain't there your carb won't give proper metering.


Regards,

Rick

 

[Thunder in NWOR]

May want to check fuel pressure between fuel pump and carb. Running on the low side, weak pump or tiny bit of air leak into line, will sometimes give you fits....

 

[Bill W]

Try retiming your engine using a vacuum gauge.
I found that both my 230's in my M-37 & WC-21 ran great at about 2°btdc and were getting a steady 20inches on the vac gauge ( this was at sea level ).
After doing both of my vehicles this way ( and tweaking the carb adjmt ) it took care of the flat spot, though ( as you already know ) being the acc pump is vac operated you'll always have a ever slight hesitation when you hit the gas.

 

[Roller]

Check the carburetor base gasket to make sure the vacuum port isn't restricted and also the crankcase ventilation valve for proper function. I just had the same issues with a M601. Turned out the problem was low vacuum at the carb. Homemade gasket restricted the port in the carb base and there was no crankcase vent valve installed.

Frank

 

[T. Highway]

I would check the base gasket 1st. Here is a picture of the correct gasket from the G741 site (2nd from the left is the correct one).
I would also set the timing closer to 4* BTDC with a timing light as a starting point. Did you set the float height at 5/64" and no lower as a starting point? How snug was the accelerator plunger in the bore?

Bert

 

[GUNNY 155]

Thanks for all the help guys. Base gasket is correct. Float level is correct. Fuel pump is new. Starting to think that this 60 year old carb is just worn out, although things seem to look good and I rebuilt it with all NOS goods. I will post the solution once I figure this out.

 

[GUNNY 155]

Results

OK guys I said I would let you know how I made out after all the suggestions. Seems in the end that my carb was either just plain worn out or too many people who were not sure what they were doing were in there before me. Or maybe just some of both. Any way the fix was a call to John at MWM and getting one of his rebuilt carbs. I attached a photo. I will also add they work just as good as they look.

 

[rchalmers3]

Sometimes throwing money at a problem works! I'm glad you got it going and thank you for the follow up posting.

Rick

 

[GUNNY 155]

Roger that. It is after all a government vehicle. So yes that would work. LOL

 

[mhassett]

Wow, this post was really helpful.
Thanks a million.
MHassett

 

[bgates]

On many of the M37 carbs I've worked on with the same problem they seem to have a non working accelerator pump. If you open the carb up and remove the accelerator pump you can see two check balls in the well. What happens is they get reversed. Someone puts them in the wrong hole. If they both come out easily they are correct but if the larger one doesn't come out it's because it's been placed in the small hole and it's a bear to get out without damaging the body of the carb. It won't allow fuel to be drawn in to the accelerator pump well from the float bowl. I made an adapter so I can use high air pressure (130 lbs) to blow into the hole in the float bowl that feeds the accelerator pump to blow the larger ball out but be careful. That ball comes out like a rocket.

 

[joseph m37]

Okay guys I could use some opinions. I have the stock Dodge 230 that I rebuilt that is also balanced and blueprinted. I have a bit of a flat spot coming off of idle. I have the timing set at about 7 degrees and hesitate to push it farther. I realized that this would be a given using todays fuels rather than what the engine was originally run on. So first question, what is being run for initial timing by you folks out there. BTW I am using 24v all GI ignition system. The advance curve on the distributor is also factory. What I am thinking is the flat spot is caused by a lean accelerator pump. The carb has been rebuilt so all that is fresh. Now I am an old muscle car guy and have plenty of experience with Holley, Carter AFB's and all the 3 duce set ups from back in the day. All those had mechanical accelerator pumps and could be adjusted as rich or as lean as you needed them to be. I have studied the info for the ETW1 on the M37 and realize that the accelerator pump circuit on this carb is vacuum operated so how well it operates is based on manifold pressure and inches of Hg. It also would be logical to assume that there is no way to adjust the function of the accelerator pump. So my second question is this. Is that flat spot just the nature of this carb? When driving I can sort of feather the gas pedal to get around it but it is somewhat annoying. Besides that my OCD side wants perfection when I have this restoration finished. So looking for any advice you guys can toss my way based of experience of solutions you have found.

7 degrees which way?,what we did with our m37s,both are rebuilt frame off, is we adjusted by vacuum,that seems to work best on these engines,put a vacuum gauge on the intake manifold and when you get the highest vacuum your good