Running Irregularities on Built M10

[CutterComp]

Thought I would start a new thread, since progress has been made since the last one and the topic is slightly different.  Again, quick recap, this is a Top End Performance fully built street motor, est 175-180bhp, twin Weber DCOE 45s, Crane Cams optical ignition module, etc.  Car sat outside 15 years, with just 500 miles on the drivetrain, I rescued it and now trying to resuscitate.  Cleaned out the fuel tank, fuel lines, new filters, rebuilt the carbs with a Redline kit.  

 

I fixed the minor intake vacuum leaks since the last thread (new gaskets and o-rings between the carbs and manifolds).  Can't say that made a big difference, but it helped some and I can cross that off the list.  I have triple checked the mechanical timing and it is spot on.  I repaired some mouse chewed wires on the Crane Cams ignition.  Balanced the carbs as best I could with a flow meter.  Idle jets are now about 1 3/4 turns out which is better than before and within the acceptable range.  Initial advance is about 15*, definitely won't run well on less.  Strong looking spark in all four cylinders.  Leak down test well less than 5% in all cylinders. 

 

So the engine still doesn't hold a steady idle.  It will idle okay for awhile but then starts to stall out and I have to rev it to keep it alive and then the idle jumps way high and hangs out there for awhile (throttles seem to snap fully closed, however).  The other big issue is that it still backfires out the intake and exhaust occasionally.  Off idle throttle response is a subjective thing (and I'm honestly not used to carbs) but it isn't great until I've revved it more than once.  Also, it has a fairly large cam (not sure which one however), so I can't expect it to idle at 800 RPM probably, but I have set the idle screw to somewhere around 1300 RPM if I want to be sure it will stay idling and not eventually stall. It can idle at 850 for short periods of time but if I don't stand ready to save it, it will stall.  Also, the engine seems to shake a surprising amount, new engine mounts notwithstanding.  

 

I do have new Bremi plugs wires, Bremi distributor cap, Bosch rotor, and Bosch plugs on the way.  All the parts currently on the car appear fine but given that they all say for 15 years, I thought I should replace them anyway and maybe get lucky. 

 

I recorded a video hoping that a video is worth a thousand words. Hopefully the intake and exhaust backfires and generally rough running come through.  Not sure how good the sound is for other people.  You can see I need to keep my hand ready on the throttle linkage to save it.  Sorry for my face captured in the video still, ha!

 

Here is the link, I hope it works: 

 

[Schnellvintage]

The valve seat(s) might have some rust on them, causing them not to seal properly. Moisture causes corrosion and havoc, to a sitting, non-operating engine. I would get one of those small cameras and try to look at the valves, pistons and cylinders through the spark plug hole. It may be other issues. Carb jetting and timing set up. Does the timing mark jump around with timing light ? Is the distributor advancing/retarding correctly? Not sticking.
FWIW




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[CutterComp]

It had a basically perfect leak down test on all cylinders so I know the valves are sealing well.  The timing mark is pretty steady as well.  Carb jetting seems right for this engine from the research I did when I had the carbs apart.  Definitely close enough for it to idle well.  Somebody suggested previously to check the advance mechanism and I did that, seem to be free and functioning correctly.  

[2002Scoob]

TBH... It sounds and runs like the one time I forgot to connect the brake booster hose and had a massive vacuum leak to where it was only firing on 3 cylinders because the back cylinder was full-lean due to the way Ireland manifolds have the booster hookup.  

 

Ergo, ya checked for a booster leak?

 

Just as a data-point... I have my idle set to 950 with my DCOE's, and advance is set at 19.5@1000rpm. 15.5@700. Might just need more advance and a higher idle. What's your AFR at idle?

Edited October 28, 2019 by 2002Scoob

[02Pilot]

Check float levels in the carbs. I'm guessing they're too high. Also possible you've got too much fuel pressure.

 

Still sounds to me like you may have a timing issue as well, but check the fuel supply first.

[Dudeland]

Firing order, or vac leak. 

[coloincaalpine RIP 2021]

Traditionally,         backfires out the carbs= lean    backfires out the exhaust= rich

[zinz]

Which plugs are you running?

 

Pull the plugs and check color and condition. 

 

I agree with Dudeland, it sounds as if the firing order is incorrect, or a massive vacuum leak (make sure the oil dipstick is fully seated)

 

Also, try pulling one plug wire at a time to see if it makes any difference in how the engine behaves.

 

As also stated above, fuel level is very important for a DCOE. 

 

Ed

[AustrianVespaGuy]

Dat thur car only be runnin' on 3 cylinders, matie, yarg!!!

[TobyB]

35 minutes ago, AustrianVespaGuy said:

Dat thur car only be runnin' on 3 cylinders, matie, yarg!!!

 

... if ye be lucky!

 

synch meter can help tell you, or even just put your hand on the header.

  The one that doesn't burn you isn't working.

 

Pull the plugs, and snap a pic-  they may tell a tale...

 

t

[rcf925]

I have a similar build with 45's and just went through this. Unplug brake booster and cap off manifold. I'm thinking Mine is also around 175 hp, I have a .292 cam, forged pistons, etc  with a head that came off race car so heavily ported. Mine ran pretty similar to yours til I figured it out. My booster when hooked up worked but I think had a leak which affected idle, There was small idle jets 50's, I put 60's in and what a difference, No stumbling off tip in, ended up with 125 mains, Pulls hard all the way through rpm's. As others have said double check firing order and timing and double check for vacuum leaks and make sure carbs are synced.  My motor shakes a little at idle at 900 rpm but will idle down to 500 easily but I keep at 900. Good luck as this also frustrated the hell out of me til I got it right

[2002Scoob]

36 minutes ago, rcf925 said:

I'm thinking Mine is also around 175 hp, I have a .292 cam

?

 

Don't wanna change the subject... but....

 

I'd agree with your suggestion of taking the booster outa' the equation. Just to be sure. 

Edited October 28, 2019 by 2002Scoob

[rcf925]

4 minutes ago, 2002Scoob said:

?

 

Don't wanna change the subject... but....

 

I didn't think it was that much either, But after driving it and several others including a couple race car drivers there guessing around 175 but I wont know til I dyno it . I'm happy no matter what it is

Edited October 28, 2019 by rcf925

[Dudeland]

1 hour ago, AustrianVespaGuy said:

Dat thur car only be runnin' on 3 cylinders, matie, yarg!!!

Yarg that be a "crusty" problem you have. 

 

[CutterComp]

Thanks everyone, a bunch of good points and suggestions here.  I will attempt to address each one as soon as I can and report back.