TR6 73 TR6 Sputtering problem?

[mabbott]

I have a 73 TR6 that ran great last year. I usually run with the choke 3/8 to 1/2 when cold for about 3 minutes driving before I can push in the choke all the way with out sputtering. It then ran fine.

Now this spring, I do the same 3/8 to 1/2 choke and drive for 3 minutes, push in the choke and it runs fine until its really warm or after 20 minutes driving....it starts to sputter. If I pull the choke out 3/8 when hot, it runs great again.

Any ideas?

 

[Guest]

Have you done any tinkering with your carbs lately? Have you kept the oil levels up? Either you are very low on oil or your carbs are set way too lean. Choking a cold engine modifies the stoichiometric fuel ratio and allows combustion more easily by increasing the fuel. When you unchoke, you are leaning out that ratio to what should be an ideal for your car. Apparently it is not. Something is out of kilter. Check your oil. Have you ever had the carbs completely overhauled. Strombergs are wonderful carbs but they do need attention now and again.

 

[achtungeveryone]

I agree with Bill, mine did that when it was low on carb oil. engine oil is fine or you can try 3 in 1 machine oil,I have used a mix of marvel mystery oil and dextron. I'm back to engine oil but may try sunflower seed oil since I like sunflower seeds so much!

Achtung

 

[mabbott]

Thank ypu for the responses.

The oil level is fine and I use Marvel Mystery oil as I did twenty years ago in my 71 TR6. I have not adjusted anything and the PO had the carbs overhauled a few years ago.

I'll try another oil for the carbs and make another test drive.

The real issue is related to the fact that it runs poorly after it is hot and requires the choke.

 

[Brosky]

Classic case of lean mixture, possibly caused by a cracked or loose vacuum line? Maybe old age deterioration?

 

[RonMacPherson]

Could also be intake manifold gasket degradation. Get a spray can of carb cleaner, with a nozzle. Engine warm, air filters removed, spray around each of the intake ports, on the head, up against the carb, takeoff to the booster, vacuum lines, etc. anywhere you see could be a leak source. If the idle increases.............

 

[Brosky]

Hey! I just noticed that you're in MA. I'm in RI, so we may be close. Are you near Providence/Pawtucket? If I can help you in any way, just let me know.

And welcome to the forum! Nice to have you here.

 

[AltaKnight]

My car did that when I had it leaned out too far.
Pull the plugs and check if you have an overly lean condition on one or both carbs.
If you have white deposits instead of tan then it's too lean.
You need the special adjusting wrench to alter it.
It can also do that if you have low fuel levels in the float bowls, that could be a sign that the float valve is sticking.

 

[YankeeTR]

Since the car ran well last year and after a several month nap it doesn't it may be an issue with debris or varnish in the fuel system.

Todays fuels degrade faster in storage than they did in the past and that degradation could be causing the problems.

I would run a strong fuel system cleaner in the fuel tank, clean the carbs with Gumout or a similar carb cleaner paying particular attention to the carb throttle bores and ports and passeages within the carb.

I always have a similar problem with the Tecumseh engine on my pressure washer. Every year it needs some choke to run properly after it comes out of storage. I always have to clean the carb with Gumout and after a through cleaning it starts to run properly again.

Perhaps you have a similar problem.

 

[gjh2007]

Temp compensators on carbs?

https://www.vtr.org/maintain/temp-compensators.shtml

 

[Simon TR4a]

I assume you are using the stock carbs, in which case I would check the carb diaphragms, they are thin rubber and may split over a period of time allowing erratic mixture.
I always look at the easiest/cheapest solutions first, then move on to the more complicated/expensive ones!
Simon.

 

[mabbott]

Thanks for all the responses. I went for a ride yesterday with fresh fuel and topped off the carb's with oil. Made it half way to work and the LBCSTB. (LBC sh*t the bed). Too soon to tell if the sputtering had changed. Got the AAA Flatbed ride home.

This time it is the ignition.....no spark (using the Pertronix Igniter). A good spark from the coil wire lead but nothing to the plugs. I am now going to order my ignition spares kit and make sure I have nominal tools on board.

Once this lack of spark is repaired I can get back to the lean carb issues. I did pull the plugs to find the are burning white at the tip.

Paul.....Thanks for your kind offer to help. I am located in Hudson close to the 495 and 290 intersection. Not that close to RI.....unless I had a good running TR....8^)

 

[DNK]

ROTOR

 

[RonMacPherson]

Like DNK said, Probably the rotor. Possibility the center terminal in the cap has fallen out, but quick visual will determine any problem with the cap.

 

[Brosky]

I know where Hudson is. I'm actually not that far away. Let me know how you make out. I have a small collection of spare parts, should you find yourself unable to get something in short order.

I agree on the rotor diagnosis and it's easy enough to check, if you have a replacement. If you can't find one, I have several.

 

[mabbott]

The rotor looks fine, I removed it and it doesn't have any cracks and the brass contact is in very good shape. The center contact on the cap is there and is still spring loaded. I believe the next step is to purchase another Pertronix Igniter. If it is bad, do they go bad often and what would cause it?

 

[Andrew Mace]

I assume you are using the stock carbs, in which case I would check the carb diaphragms, they are thin rubber and may split over a period of time allowing erratic mixture.
I always look at the easiest/cheapest solutions first, then move on to the more complicated/expensive ones!
Simon.

I'm with Simon here...although subsequent posts from you make me wonder if the ignition might have been the cause all along. Regardless, I'd pop the tops off the Strombergs and check the diaphragms for splits. In an "emergency" situation, small tears can be temporarily patched with some of that plastic electrical tape!

Back in the 1970s, when I used my GT6+ as a commuter, rallye and autocross car 24/7/365, I would get about a year out of a carb diaphragm! Annoying, but ultimately easy to diagnose and fix! /bcforum/images/%%GRAEMLIN_URL%%/hammer.gif

 

[mabbott]

Well, the dead ignition/no spark to the plugs was found.......DNK, you were correct, the ROTOR. I purchased an entire tune up kit and tried the simple things first and the [censored] rotor was the culprit. I don't understand how a perfectly fine looking rotor can instantly go bad.

As for the sputtering / lean condition. I looked at the diaphrams and they look brand new and no pin holes. However, I did find a suspect cracked rubber plug on the top of the forward carb (Strombergs). I made a temporary plug and will test drive when the rain clears out of New England....perhaps Sunday.

Thanks for all the suggestions, I'll follow up on the results of the sputtering/lean issue.

Mark