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Dieseling... et al

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ronzet

ronzet

Jedi Knight
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Hey guys,

Having put about 400 miles on my newly rebuilt B engine I must say that it is running very well.

However, two things are irritating the crap out of me...

1) ONCE IN A WHILE, I find the engine dieseling (running on) after I shut it off

and

2) It is difficult to start when <span style="text-decoration: underline">warm</span>. It will crank and crank and not start BUT will fire off immediately if I roll and pop the clutch...

Any suggestions???
 
I solved my dieseling, or run-on, by always using 89 octane gas. The Lower grade 87 always cause it to run on.
 
Jay,

I run top grade in the B... I think it is 91 octane....
 
Carbs may be set too rich.
 
Tim,

Me thinks you may be right... Mileage is pretty bad as well...

I have left the jets at two turns down from flush... perhaps a bit of leaning may do the trick....

Thanks for the recommendation. I will give it a try...
 
Check all the normal tune stuff.,,, Torque head, reset valves, set timing and be sure the mechanical advance is working, check and reset carb settings. Be sure the float level is not set too high and keep your idle as low as possible.And with 400 miles put a wrench to any fastener you can as a check. Bob
 
Ron, the "basic" start setting is 12~13 "flats" of the jet from flush. You're decidedly rich with two full turns.

Get a "ColourTune". It's as accurate as anything else for dialing in a good mix setting at the bottom end. Otherwise you'll be spending tons on CO meters and two gas analyzers. No point, as the machine you're analyzing ain't that sophisticated.

:thumbsup:
 
DrEntropy said:
Ron, the "basic" start setting is 12~13 "flats" of the jet from flush. You're decidedly rich with two full turns.
Click to expand...
I thought two full turns was 12 flats?

No addressed the occasional warm start problem. I don't have that problems, but others mentioned it before and I don't recall a consensus on the cause.
 
"basic" being operative... the start point.

And 93 octane would be better, too. IF you can find it "out there".
 
Jay and Doc,

Thanks for the comments... I will be going through the normal checks this weekend... Ya' know, tighten this, lube that, adjust something else, ad infinitum...

Although I have the jets at 2 turns (12 flats), it does seem to be a little rich... so a bit of leaning is in order...

I also whacked my exhaust on a #)($* speed bump this morning... 'tis a little louder sooo that needs to be fixed also...

Be well...
 
Higher octane should help with dieseling. Too rich condition may cause hot start problem. 12 flats is two full turns, but what about the needles or the jets? I've had problems with rich condition at 12 flats, although not had any hot start problems--mainly poor mileage.
 
You may have some carbon build up on the piston tops which will raise the compression ratio slightly, but will also cause hot spots which will allow the engine to continue running. Try shooting a fine mist or spray of water into the carbs with the engine running. This usually will break up or shatter the carbon. In my experience, this usually works.

Alternative solution is to remove the head and decarbonize the old fashioned way.
 
Also check exhaust valve clearances. If they're a bit tight, you can get incandescence on the valve perimeters, and run like a glow-plug engine.
Also makes a mess of valves and seats, in time. Don't ask how I know, but I was very young at the time.
 
Gentlemen,

Thank you for the varied suggestions....

A few comments... The complete engine rebuild has about 450 miles on it... About 100 miles ago I retorqued the head studs.. breaking one (it is a new set from Moss). I removed the head, checked the cylinder and valve conditions (no carbon buildup but a bit of normal ), replaced the stud, head and gasket and re-torqued... 150 ft/lb.

I am still running natural oil (rather than synthetic) until the engine has about 1500 miles on it and the rings have seated well.

The carbs are newly rebuilt with new jets and bearings....

The valve lash needs to be checked anyway although the tappet noise is minimal.

Engine runs cool (double row radiator). Since the WT gauge is inop, I check it with a thermometer in the radiator neck... usually around 160 degrees after driving around... <span style="font-style: italic">This may be indicative of a too rich mixture or checking it at the coolest spot in the system..</span>

Oil Pressure at 60-70 at 4.5K+ rpm and 40-50 at idle of 900 rpm...

In general it is running very well...Idles no rougher than any other B I have had, Accelerates smoothly, Holds 70+ mph at ~5K rpm without a wimper and still has some pep at the high end...

I guess I shouldn't complain... but the dieseling and warm start (that is mearly an inconvenience anyway) is a blemish that I want to fix...
 
Colin,

Please forgive my ignorance... 'cc' ???
 
"CC'ing a cylinder head is a process that measures the volume of the combustion chambers in the cylinder head. The term CC'ing is the cubic centimeters of the pocket (combustion chamber) around the valves. the purpose of cc'ing the head is to determine the compression ratio of the engine. You cannot compute the compression ratio if you do not know the size of your combustion chambers. Also it is important in performance heads to have equal cc'ed heads to balance the engines compression to each cylinder. "


Found Here.
 
Simon,

Thank you for elucidating me to a term with which I had a passing aquaintance..... :smirk:

To answer the query... ah, no I did not 'CC' my head... the dieseling is an infrequent occurance and did not, to me, warrant the additional expense associated with the process... :rolleyes:
 
In what shape is your carbureator heat shield?
 
Tony,

Thanks for the query...

The heat shield is in place and, with the exception of a small crack 3" long from the bottom up below the rear carb that causes a SLIGHT distortion, it is in good shape...
 
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