Coughing car

[Tim Sture]

I have a Vx 1600 8v (twin carbs) and last Saturday was doing a airfield track day (at Elvington near York). The car ran perfectly during the first couple of sessions but (after I'd got the tyre pressures sorted out) on my third foray it started misfiring badly through the fast right hand corners (ie, sustained relatively high g). It was absolutley fine through left handers and in a straight line but would not continue to pull through any long right handers. bit of a problem on a clockwise course.

 

I thought it may be because I was low on fuel so filled up and returned, to find exactly the same problem. Simon Scott may have the flames and smoke (black and white) from the exhaust on video....

 

Anyopne any ideas what the problem may be? Is it just that the carbs need adjusting (it's about 10 months since they were last done, as part of a service)? Amy other ideas? The car ran fine on the way home (left early to avoid damage and also cos there was no point spluttering round the track).

[stevefoster]

Check the floats for free movement / play (a 1/8" drill comes in handle to measure clearance if memory serves). If the floats were sticking under g force you would temp run out of fuel in the corner. This could only be one carb and hence the misfire effect.

 

Do you have an electric fuel pump? If yes then do you have a pressure reg fitted?

If you don't then surge could be an issue under cornering. But I would check the floats first.

 

[John E]

Afternoon Tim,

Yes it was me who passed you and Julian on Saturday morning. Tad misty on the top dont you think. We were on our way to the ELMS at Donnington.

Now back to your carbs. I had exactly the same problem with mine and it was float levels. I've had two pieces of ally rod turned down, one for the open and one for the closed float positions. The are very different in size and take a little setting up. Its easy to take the chamber tops of the carbs and if you follow the instructions, which I also have, then its a doddle. Will Sunday be early enough or do you want to have a go at them earlier cos if you do I can post the measuring rods from the office tomorrow along with the instructions.

[Andrew Russell]

Hi Tim

Thanks for the e mail....it's good that we have now established how to contact each other properly at last...a little late, but there's always next time!

 

Sorry that you had problems on the day..

 

When I read your e mailed desciption of your problems, I thought that it sounded like either float level or fuel pressure, so I would simply concur with the suggestions already posted by Steve and John.

 

See you soon.

 

Andrew

[Red SLR]

Tim

 

I cought a flame that was about 6 foot long on video!! Unfortuinatly the quality is crap as I was getting loads of vibraiton through the camera.

 

Hope you get it sorted soon. All the best simon.

 

Ps

 

It rained for most of the afternoon and the track was like ice(on slicks by then). i had 3 or 4 spins, at over 80mph..... including one on the back straight which left me facing the wrong was with a Nissan 200 SX coming towards me at about 90 ish. So I headed off at about 330pm as it was getting to dangerous. But a very good day was had. Simon.

 

X777CAT

[Andrew Russell]

You chaps were just unlucky with the weather on Saturday....Friday was gloriously sunny and warm and Sunday wasn't too bad although cold.

 

Saturday was a little wet though!

 

Andrew

[Red SLR]

Andrew

 

Did u go on Sat?

 

Simon.

 

X777CAT

[Tim Sture]

Thanks for the help chaps

 

Simon - if there was a lot less grip in the afternoon maybe I should have stayed, with less g I might not have had the same problem! Mind you, I still managed to get quite wet just from rain on the M61 so I would have been soaked if I had stayed longer at Elvington.

 

John - no hurry - Sunday will do fine - the car is OK for general road use, so I can just pootle along at the back OK then anyway!

[Graham Perry]

Something else that can cause a mystery misfire that is carb related is a largish brass retaining screw/bolt for the inards of the carb. They are underneath each barrel. If they fall out, which they often do, you will develop a misfire. Most racers wire these into position to stop them dropping out.

[Andrew Russell]

Simon,

No, I didn't make it on Saturday, I spent most of the day fettling the car and it is now almost ready for the Summer, just needs an MOT which should be done this Saturday.

 

All I want then is good weather..........

 

I am glad to hear that you all had a good, if a little damp, time at Elvington, and hope to meet up with you soon, on one side of the Pennines or the other.

 

Keep the LAD updates coming and I will try to tag along on one of your jaunts..

 

Andrew

[Pierson Broome]

My x/f displayed exactly the same symptoms on my first track day at Goodwood a few years back - I had a mechanical fuel pump at that time and this wasn't up to the job of supplying sufficient fuel to the carbs. on faster right hand corners.

 

Changing to a regulated electric pump cured the problem. Be very careful if continuing to run lean - you could end up doing some serious piston damage.

 

Pierson