TR6 TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, repeat

[Michelotti]

TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, repeat

Okay, so at first I'm thinking vapor lock, right? I mean it runs great. I can shut it down & re-start with just a touch of the starter. It'll never stop unless I turn the key off, no stumbles or rough running. If I let it sit for more than a few minutes... nothing. Not one cylinder will fire. If I let it sit overnight, its stone cold, still nothing. Not one cylinder will fire. If I come back the next weekend it'll fire right up! This is a verifiable, repeatable pattern now for 3 weekends.

Engine had been sitting for 8 years prior to a few weeks ago. Lots of power (CC# block from a TR-250 now in the TR-6), but blue smoke abounds after warmup upon acceleration. Cheap Harbor Freight compression tester shows approx 95 psi across all cylinders. A squirt of marvel mystery oil in each cylinder will maybe bump the compression readings 2 psi.. Very puzzling compression readings when taken in the context that it'll snap my head back with powerful acceleration on the road. Haven't taken the valve cover off yet to see what might be going on there.. valve cover breather open to atmosphere.. big time exhaust manifold leak at flange joining to exhaust pipes..

I'm thinking of cleaning out & rebuilding the ZS 175's as a first step. Any and all troubleshooting ideas appreciated!

 

[poolboy]

Re: TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, re

Snaps your head back when you accelerate !!
Are you sure you have a Triumph 2.5 liter engine in there ?

 

[trrdster2000]

Re: TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, re

Michael, check the ground wire on the distributor plate for continuity and the one to the points.

Wayne

 

[TR3driver]

Re: TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, re

Sure doesn't sound like carburetion to me. And even if it was a problem with fuel delivery to the carbs, it would be hard to start (have to crank until the bowls fill) after the waiting period.

I would be troubleshooting the ignition system first.

Have you checked the valve lash? How stock is the engine? (Low compression plus great performance suggests a different camshaft, etc.)

 

[glemon]

Re: TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, re

The overnight vs sitting a week thing is the real puzzler, if it is the old intermittent crud blocking fuel delivery you are usually good to go after 10 or fifteen minutes, but otherwise acts as you describe, I still wouldn't rule it out.

If it is a heat related electronic intermittent like the coil or condenser it should certainly be cooled off after an overnight sit.

I once had my TR4A arcing on the cap )or maybe coil, long time ago, but know it was arcing related to an oily surface) because of oil on it, far fetched, but oil getting on the ignition and taking a week to flow off.

You will need to do more diagnostics, check for spark and fuel (easy, pull the fuel line, have wife/friend/neighbor crank it over, should spurt spurt spurt) when it doesn't work to at least start to narrow things down. Assume you are still using the mechanical pump, or would put an intermittent electrical SU pump in the mix.

 

[Michelotti]

Re: TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, re

Michael, check the ground wire on the distributor plate for continuity and the one to the points.

Wayne

Wayne I think you've hit upon it! The ground wire is loose with insulation rotted away. After tightening it fired right up. I'll need to replace it for sure.

 

[Michelotti]

Re: TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, re

Sure doesn't sound like carburetion to me. And even if it was a problem with fuel delivery to the carbs, it would be hard to start (have to crank until the bowls fill) after the waiting period.

I would be troubleshooting the ignition system first.

Have you checked the valve lash? How stock is the engine? (Low compression plus great performance suggests a different camshaft, etc.)

Looks like it's an ignition issue as suggested, I think we've hit upon the solution with a new distributor plate ground wire.

As far as solving the issue of burning oil, I'll check the valve lash as suggested. The engine has had work performed on it by the PO. Unfortunately I never had the opportunity to speak with him since the TR-250 was purchased from an intermediary dealer. The dealer said he thought the engine was bored & had a mild cam installed.. makes sense from what we know so far..

 

[Michelotti]

Re: TR-250 CC engine runs great, then nada, wait > 2 days, then runs great again, re

The overnight vs sitting a week thing is the real puzzler, if it is the old intermittent crud blocking fuel delivery you are usually good to go after 10 or fifteen minutes, but otherwise acts as you describe, I still wouldn't rule it out.

If it is a heat related electronic intermittent like the coil or condenser it should certainly be cooled off after an overnight sit.

I once had my TR4A arcing on the cap )or maybe coil, long time ago, but know it was arcing related to an oily surface) because of oil on it, far fetched, but oil getting on the ignition and taking a week to flow off.

You will need to do more diagnostics, check for spark and fuel (easy, pull the fuel line, have wife/friend/neighbor crank it over, should spurt spurt spurt) when it doesn't work to at least start to narrow things down. Assume you are still using the mechanical pump, or would put an intermittent electrical SU pump in the mix.

The fuel line was plugged up after an 8 year nap & I had to replace all fuel lines along with blowing out the remaining crud from the tank with compressed air. That's why I was leaning toward carburetor rebuilds as the final piece of the fuel system not yet investigated. The mechanical pump seems to be fine, it primes in a heartbeat.

As I was just troubleshooting the distributor ground wire issue I noticed a couple of the distributor cap's rotor contact points were worn (gouged) away. Very odd.. I guess I must've fastened the cap improperly at some point in the past.. I just ordered a new cap, coil, spark plug wires, & condenser tune-up kit from TRF.