New engine gremlins - frustrating

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TRWRacing

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New engine is in but some gremlins:

MRL 360 Crusier. See Dyno sheet
1973 Dodge Dart Sport 340 - H code

Per my engine builder Mike (MRL)
Cam specs: 284/228 .480 lift 112* LSA 108*

Running stock 340 exhaust manifolds, want the stock look for now. Headers later possibly.

There is a slight flat sport low speed idle carb backfire that occasionally occurs.
The carb is a Summit 750VS. Upgraded the carb accelerator squirters via the Summit carb tuning kit from .035 stock to next size .37 didn't seem to mae a difference. Assuming to go increase to the .040 or .42. Timing good. FBO ignition from MRL with stock recurved distributor

During install called Turbo Action and spoke to Paul for a recommendation on a new torquw converter based on my specs and during style. Weekend cruiser and race 1-2 the season at the strip. I don't know the p/n as the installer still has the paper work and the car.
It is an 11" TC with 2500 stall. I need to call Paul, but I am assuming it's a 17801 S800, but the installer has the box/paperwork.

Seems to not have as much low end power from a stand still. Stock 340/727 trans would spin the tires 235/60 R14, seems to have good power once moving 20+ mph

Everything installed, couple of test drives and the heater core now leaking, so that will come out.

Any advice to cure these last issues, much appreciated.

Thanks,
Eric

Dyno sheet.jpeg
 
IMHO, that cam is not going to be all that torquey at low RPM's. At 20 mph, and the TC locked, then engine would be turning around 2600 RPM, assuming a 3.55 rear gear so it is making sense that things are starting to work at that speed; the cam is getting up on the curve.

Got any piston info for the new engine? CR is unknown at this point.
 
nm9stheham said:
IMHO, that cam is not going to be all that torquey at low RPM's. At 20 mph, and the TC locked, then engine would be turning around 2600 RPM, assuming a 3.55 rear gear so it is making sense that things are starting to work at that speed; the cam is getting up on the curve.

Got any piston info for the new engine? CR is unknown at this point.
Click to expand...

Sorry, I don't have the paperwork with me, but I seem to remember Mike (MRL) saying the compression is little over 9.0
I am new to this with performance upgrades.. I just want to make sure the TC is good for what I have and not causing any additional problems. It's mainly a weekend cruiser. The rear gear is the stock 3.23

We are on the right path with the carb lean and the squirter upgrade? Just increase the discharge size.
 
Is the carb on the engine the one used for the dyno? if not ask MRL what was used with acc and jetting
 
check ign. voltage it might be low, do you have full voltage to the coil?
 
There is a slight flat sport low speed idle carb backfire that occasionally occurs. Backfire is a red flag!
What's the ignition timing and curve?
You need to get ignition right before carb changes.
what's the rear gear and tire size?
 
mderoy340 said:
There is a slight flat sport low speed idle carb backfire that occasionally occurs. Backfire is a red flag!
What's the ignition timing and curve?
You need to get ignition right before carb changes.
what's the rear gear and tire size?
Click to expand...

This only happened 2 twice in a 5 mile test drive and never from a standstill. It happens not always after coasting, make a turn, feather the throttle, carb stumble at 5-7 mph, pop/backfire through the carb and then takes off.

Ignition is the FBO system provided by MRL with FBo ignition box and ballast resistor bypass jumper installed.

The distributor curve was done at MRL. Total was 36* at 3000rpm with the vacuum advance disconnected. I don't have the dyno sheet with me but I believe the initial is 18*

The guy working on finishing it says timing is good and is ASE certified with over 30+ years experience and works on older classics. He is old school. I had a '71 Demon with 318 Rochester that acted the same way with a carb that went away with a Carter. I found out later that was a Chrysler TSB on that carb in '71.

Rear gear was stated up in the thread 3.23 and tires 235/60 R14 rear front 215/70 R14
 
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TRWRacing said:
This only happened 2 twice in a 5 mile test drive and never from a standstill. It happens not always after coasting, make a turn, feather the throttle, carb stumble at 5-7 mph, pop/backfire through the carb and then takes off.
Erratic fuel pressure and float level may be the problem.

Ignition is the FBO system provided by MRL with FBo ignition box and ballast resistor bypass jumper installed.
Check your firewall connections are clean.

The distributor curve was done at MRL. Total was 36* at 3000rpm with the vacuum advance disconnected. I don't have the dyno sheet with me but I believe the initial is 18*
FBO always has a curve sheet and specifies if hooked to manifold or ported vacuum. IMO if your at 18* you want to run manifold vacuum to bump up idle timing.

The guy working on finishing it says timing is good and is ASE certified with over 30+ years experience and works on older classics. He is old school. I had a '71 Demon with 318 Rochester that acted the same way with a carb that went away with a Carter. I found out later that was a Chrysler TSB on that carb in '71.

Rear gear was stated up in the thread 3.23 and tires 235/60 R14 rear front 215/70 R14
Click to expand...
You should be able to fry the tires.

You may have gone the wrong way going bigger on the pump nozzle. Put the 35 nozzle back in and see what happens. If it gets better put a 33 in. Use the smallest pump shot you can without stumble. Any throttle movement and you should have instant shot.
 
Flat top pistons .010" below deck and some fairly standard parts (heads and head gaskets) give an 9.1 SCR, and, with that cam (MP 284 cam as a guess, installed with 4 degrees advance), DCR computes to be 6.9-7.0. (If I am getting this wrong, please someone correct me....)

With a 3.23 rear gear at 20 mph, the engine will be turning around 2300-2400 RPM, around where the TC is starting to lock. From the torque and HP numbers, it would seem that the engine would be coming up on the curve at 2400 RPM. But IMHO, that cam is not going to be a low end torque cam.

Is the low end lack of torque consistent, and separate from the occasional hesitation? If you floor the car at low speed, where does the tach end up as it moves out form a standstill?

You could go up to a 2800 or 3000 RPM stall, but then at cruise at 60 MPH, the engine will be wanting to be at 2600 RPM, below the stall speed for a standard type TC. A rear gear change would do better for you, IMHO.
 
Thanks. Just FYI. MRL included a new Carter fuel pump . I have not had the chance to check at WOT or take note of the tach firing a test drive yet . I am not picking up the car until it's complete. Lack of torque seems to consistent. I haven't turned wrenches on car like this in 25 yrs., but if it was timing it would seem to do it at every stop light.

The distributor was removed to assist with install, but was marked prior to remove and reset.

If it's the rear gears ok, that I can live with
just like to get it drivable and bring it home. The installer has had it for 8 weeks and it's been a year and driven it 200 miles. I would like some closure before winter.
 
TRWRacing said:
The distributor was removed to assist with install, but was marked prior to remove and reset.
Click to expand...
IMHO, that calls for rechecking the timing, especially if there are any questions on performance. It does not take much movement (like the width of a mark) to move the timing several degrees with any distributor; a 'hard to see' 2 degree change in distributor position would give 4 degrees of change in timing. It just seems like common sense to recheck this in detail with the symptoms.
 
My mechanic said timing was off too advanced after he removed the distributor and installed. It had some kick back initially on startup 2 weeks ago. He corrected that, but now since test driving it has had the occasional bog at light speeds. He is thinking a lean carb situation.
 
TRWRacing said:
This only happened 2 twice in a 5 mile test drive and never from a standstill. It happens not always after coasting, make a turn, feather the throttle, carb stumble at 5-7 mph, pop/backfire through the carb and then takes off.
Click to expand...
Just checkin' the obvious which you probably have already done: Have you checked the float settings? That is always 1st; that effects all phases of carb operation.
 
I believe he did that as well early on in the troubleshooting process cause he did mention that.

When it does happen it's always with light throttle at low speeds.
 
TRWRacing said:
My mechanic said timing was off too advanced after he removed the distributor and installed. It had some kick back initially on startup 2 weeks ago. He corrected that, but now since test driving it has had the occasional bog at light speeds. He is thinking a lean carb situation.
Click to expand...
OK, I am inclined the same way, but timing can combine with lean/rich carb conditions to produce symptoms like this. I too am inclined towards a lean condition, but would be looking more at secondary throttle plate settings and things related to the transition circuits for such a random thing. Did you say it only happened after coasting through a turn, or did you really mean to say 'not always' after a turn?
 
TRWRacing said:
My mechanic said timing was off too advanced after he removed the distributor and installed. It had some kick back initially on startup 2 weeks ago. He corrected that, but now since test driving it has had the occasional bog at light speeds. He is thinking a lean carb situation.
Click to expand...

From my experience, a lot of mechanics will set the timing at the stock initial setting, and have no idea that a performance tune often has the timing significantly altered from the stock settings. Double check to see that your initial timing is set at 18 or even 16 if you are getting kick-back. Some people just never get the whole timing thing.
 
nm9stheham said:
OK, I am inclined the same way, but timing can combine with lean/rich carb conditions to produce symptoms like this. I too am inclined towards a lean condition, but would be looking more at secondary throttle plate settings and things related to the transition circuits for such a random thing. Did you say it only happened after coasting through a turn, or did you really mean to say 'not always' after a turn?
Click to expand...

From what I notice it has been coasting/slowing down after completing a turn and then apply light throttle at about 5-10 mph. It stumbles/chokes to almost dies, pops back through the carb and takes off. A turn might be a coincidence just because of the low speed conditions. I'm incline to say that I have only noticed it after a turn, but I only test drove it for 5 miles.

I have not seen it occur off idle from a standstill.

I will check with him on the timing this week. He has in the past worked on performance Chevelles that I have seen in his shop. Weather getting crummy in Chicago and not the ideal time to do this. Engine was delivered at Labor Day.
 
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Just some random thoughts FWIW:
- I have to wonder if everything was well warmed up in only 5 miles.
- IMHO, tuning out this relatively small symptom would be down on the list until there was several hundred miles on the engine.
- With the center hung floats, the corners should have less/no effect on fuel level in the carb bowls, but speeding up/down may effect it.
- Does this have an Air Gap intake? Not the best for a cool engine in cold temps.....
- Consider putting a vacuum gauge on the engine and watch it to see what the vacuum levels are when this happens; it may give you an idea of what carb operation is in play when it happens. For example, it may tell you that the vacuum is dropping to where the vacuum secondaries are wanting to blip open for a moment; it would only take a hair of secondary opening to lean things out.
 
Engine was fairly warmed up by the mechanic prior to my arrival for the 5 mile test drive, but all points valid.

If timing is 16-18* is set and with increase to .037 nozzle discharge size. Would an increase in next size in jet?

Yes, it is an air gap intake, but this car is a weekend summer driver only.

Vacuum gauge is a good idea to see what happens.

Interest tidbit on that '71 318 Rochester 2bbl issue lol

IMG_8199.JPG
 
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FWIW, I personally would not be working on the jets at this point; if you are getting this with just light throttle, then the primaries are not really in operation. I would be:
- raising the primary float level temporarily to see what happens; this is not really for a fix but to obtain clues as to which way to go with other things
- looking at vacuum levels to determine operating phase of the carb when this occurs
- adjusting the secondary idle stop screws (assuming this carb has one, which, being made by Holley, seems likely).
 
Good point. I wish it was done in September when all the parts where there and weather was summer like.

The first test drive last week it was 70*
Friday's test drive was 60*. Certainly it's been a jerky motion lean bog with carb pop at light throttle 5-10 mph.

Plenty of time was given to the shop to complete this while the weather was good. I really don't feel like paying the labor to readdress this next summer. I will fix the heater core then. My feeling is this should have taken 2 weeks not 10.
 
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Maybe stiffer spring for the secondary? Possible that it's opening too quick causing the bog? If so, does anyone know if it uses the same as the Holley kit? I don't see one specific for the Summit carbs.
 
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