Hesitation at Acceleration

[Aldwyn]

Hey guys!

As mentioined, I bought a 76 TR6 recently. MAN is she a blast to drive!! I think I put 300 miles on her over the weekend.

BUT...

I am having an issue with it that I am not sure exactally where to go with at this point.

After the car warms up, it hesitates on acceleration (any gear). And if I drop the OD in, it gets worse.

During the first 20 minutes or so of driving, she drives fine (including OD).

A neighbor (who owns 6 British cars!) and I spent several hours tuning and cleaning the carbs to see if this would help. No dice. I even ran it without the air filters to be safe.

Checked the points... looked good. As did the cap and wires.

We pulled one plug and it was gapped correctly, and looked brand new. (I was thinking of replacing them all, just to be safe)

Fuel filter looks clean.

Starter is new (but still could be bad I suppose), and the fuel pump looks new as well.

Any suggestions on what to try next, or what it could be?

Someone suggested water in the fuel line, and to add a water evaporator/fule line cleaner to the tank to see if that would help.

Any help would be apperciated!

Thanks!
Aldwyn

 

[Mickey Richaud]

They ARE fun, aren't they?

What color are the plug tips? You say they appear brand new. They should have a brownish tint to them. Sounds like it's running lean, which could be either a carb or timing issue. The fact that it happens after it's warmed up seems to indicate that when the choke is off is when the problem occurs.

Mickey

 

[Mickey Richaud]

Oh, and running without the air filters can make it leaner still!

Mickey

 

[Aldwyn]

I will check plug tip color tonight... can't remember the color off the top of my head.

The choke is indeed off when it starts to miss/hesitate, but it's usually off for some time before it happens. I tend to run with the choke half open (or so) for the first few minutes of idle and then driving, and then have it closed for the next 10 or 15 minutes before the hesitation starts.

 

[Mickey Richaud]

Easy test: When it starts to miss, pull the choke out and see if it smooths out. If so, then it's more than likely too lean.

Mickey

 

[Geo Hahn]

What weight oil is in the carb dampers? Some people run very thin oil (ATF, Mystery Oil) which works for some but can thin out too much as the engine warms up. It only takes a minute to empty those reservoirs and try a heavier oil (whatever you use in the crankcase might be a place to start).

 

[Aeroken]

I'd suspect the ignition coil or possibly the wires. I've had old coils work fine when cold but begin to break down when the underhood temperatures get hot.

Ken

 

[Guest]

If it is too lean, you will be running too hot as well. How is your temp gauge showing. Excessive overheating is damaging to your engine. Try giving the carbs a slight twist with the allen wrench.


Bill

 

[Aldwyn]

Ok, only had a sec to try to get a plug off, and I can't find my plug adapter. /ubbthreads/images/graemlins/frown.gif Gotta dig around. Working from home tomorrow, so will look again tomorrow.

Bill, temps are fine... no overheating is going on, including the 1.5 hour highway trip on Saturday and the short trips around town.

 

[philknight]

Aldwyn,
It might be worth your time to run it down to Mountjoy's.
They can adjust your carbs with an analizer, diagnose your problem if thats not it, do a quick safety check and give you an appraisal of your cars value for insurance purposes.
I had to take mine down there once this past year for an issue that I had (crimped fuel line that Bill nailed and I couldn't find) and having them go over the car gave me some piece of mind and some ammunition if some yuckapuck rear ends me as to the replacement value.

 

[Aldwyn]

Hey Phil!

Afer my POs experience with Mountjoy, I hesitate to use them... though his experience is odd since so many other people have been happy with them.

But taking it into the shop will be the last ditch effort if I cant figure it out on my own (with some help from Sherman, the guy down the street).

Looks like I have to go buy a new plug socket, too... I can only find my 5/8th one. /ubbthreads/images/graemlins/frown.gif

 

[bobh]

Aldwyn, Adding to Geo's comment about the damper oil... Is the damper oil gone after a short time? If the o-ring on the needle holder is bad the oil will leak past. Lack of oil in the dampers allows the air valve to rise faster than it is designed to rise. This creates a lean condition when you accelerate. The air valve rises too fast for the amount of fuel that is introduced into the stream. Check the oil, try a heavier oil as Geo mentioned.

 

[Aldwyn]

Ooops! Sorry, forgot about the damper oil!

Carbs have plenty of oil in them... just checked. The oil I am using is "Penrite Damper oil for SU and Stromberg Carberetors".

It's fairly thin stuff.

I have no clue what is in the crankcase, or even what I should be using, honestly!

 

[Mickey Richaud]

Crankcase should be good ol' Castrol 20W50. And if the dashpot oil is too thin, try the same there.

Mickey

 

[Aldwyn]

Ok, took a spin with her up to the parts store during lunch to get a new socket... she drove fine there. Temp guage never got higher then the first mark. I wonder if the temp guage is broken so she wont go any higher?

Anyway, on the way back, she started the hesitation again. Some new info:

Pulled the choke out half way, and it made no difference.

But, the hesitation almost stops above 3K rpm. I still get a little here and there, but she smoothed out above 3K. I hadnt noticed that before.

Once the engine cools down, I'll pull a plug or two and check the tips.

- Aldwyn

 

[Aldwyn]

Forgot to mention... puled a plug after the car cooled down. Plug tip was a light gray. From what I can see from reading online, this is the normal color for a used NGK plug. But I have also read that gray means running lean. <shrug>

 

[Harry_Ward]

Aldwyn,

Not too knoweledgable about the 6 but did you check the timing at idle and especially the vacuum advance timing? Also what type of ignition system does this car have (points or electronic)and what manufacturer type? Some dist. types had problems from the factory and aftermarket fix's were almost as bad. Any rev limiter attached? Is the condensor new? check or replace low tension wire? Can you ask the PO if he had the problem in the past? Is the fuel line or filter too close to a heat source? Is the filter new? float height incorrect or one float leaking (ok guessing at hard ones now and is my last thought but not likely) Keep looking it's apparantly caused by something getting too hot and you will find the problem eventually.

 

[Harry_Ward]

tan brown good, light gray lean but OK, anything white, insulator cracked, or plug electrode gap bridged not good and way too lean. You should check them all or at least one from each carb intake set.

 

[philknight]

Aldwyn,
Do your vacuum lines run into a switch that is in line with your cooling lines/hoses? If so try bypassing that switch and see if that makes a difference. Or if you'd like bring it up my way and we could switch out things one at a time and see if we can track it down. Sherman lives down the street from you? Your lucky TR stars must be lined up.
I'm an OK parts changer, He's a local legend. I've got spares for electrical and vacuum lines/fittings etc.

 

[Got_All_4]

Look for vacuum leaks or blockage in the line from the intake manifold to the distributor. During initial warm up the carbs advance the throttle and enriches the mixture. Try puling the choke out all the way when the engine is warm. It's got to be timing or mixture. Or possible both.