TR4 on strombergs

[hooperman46]

I managed to overall my strombergs a couple of years ago and the car goes very well, especially over about 2000 rpm. Under that, especially when cold, the engine is quite rough and noisy (people think its running rich but I think lean). A little choke helps a lot at the lower revs.

Do I need a different needle profile? Do I remember correctly that needle choice is limited with strombergs?

I wouldn't want to loose the good running at higher revs.

[ctc77965o]

Hi Hooper,

 

I have Strombergs on a Jag and have always been very pleased with their function & stability...slightly later type than yours, but still a ZS175xx type.

 

You say 'people think its running rich' ....why is that?

 

My suggestion would be to firstly triple-check the airflow balance of the carbs, use the hiss method, or the airflow gauge...or if you wanna go hi-tech try the dial gauge method:

 

After thats right I would open both carbs and use a vernier caliper to measure the jet position in both carbs. Since you think it's running lean at low revs, then I would make both jet positions the same by adjusting the 'higher' one to match the 'lower' one (lower jet is richer). Keep track of your before-n-after jet position figures in case you want to revert settings ..[i believe your carbs are adjustable jet, right? Later stroms are adjustable needle]

 

Now reassemble and try it...it could be that your low rev misfire was due to poor balance.... if it's still rough at low revs and if pulling the choke still makes it smoother then I would adjust both carbs richer equally, 1/4 turn of the adjuster at a time..see if you can find a sweeter low rev performance.

 

I wouldnt consider needle change yet...On a standard engine and standard carb there's no reason for the mixture/revs/airflow ratio to change...in fact older/worn needles are likely richer at idle than they were new...so if your problem really is weakness at low revs then a new needle might make things worse

[RAHTR4]

Hi,

 

I wonder if both the diaphragms are sound with no small splits...?

 

It would appear that at least four variations of the Stromberg carbs were fitted during the production of the TR4 and TR4A and each carb type was fitted with a different metering needle.

 

Thus it might be prudent to confirm which carb type is currently fitted to your car and also if the needles match the original specification.

 

I have data sheets that provide all the details to check against.

 

I can forward these as PDF's if you send me a PM with an e-mail address.

 

Regards, Richard

[boxofbits]

Hi Hooper

 

I would first check that your needles/jet is central by lifting the piston with either the lifting pin or manually and ensuring it drops properly to the base. Also top up the damper with the correct oil.

 

It sounds like you might need to richen the mixture by screwing the jet down, but I'd also check you do not have an air leak through the inlet manifold somewhere before adjusting.

 

Regards

 

Kevin

[ChrisR-4A]

Hi Hooper, sounds like you could be drawing in air. Try setting tickover at about 900 and squirting some thick gear oil around the throttle spindles. If the revs change then spindles are leaking air. Other source of air leak is inlet manifold to cyl head joint, some of the gaskets are very poor, I replaced mine, fitted with wellseal on all faces and then retorqued twice after first two outings before getting a good seal.

Also check mounting faces of carbs are flat.

Chris

Edited September 24, 2016 by potts4a

[hooperman46]

Thanks guys, a lot to think about.

I replaced all service parts including diaphragms and used new jets , the only ones available at the time (but that's all old mans memory!!!)

The carbs are CD175 , original equipment I think. They are balanced (or were balanced) with an air flow meter and as I said run very well from medium throttle onwards.

First job seems to be check physical alignment etc and then check for air leaks etc.

The only engine mods I know about ,and they wouldn't effect this problem, were the extra oil feed to the rockers, and hardened valve seats, both before I bought the car.

[stuart]

Thanks guys, a lot to think about.

I replaced all service parts including diaphragms and used new jets , the only ones available at the time (but that's all old mans memory!!!)

The carbs are CD175 , original equipment I think. They are balanced (or were balanced) with an air flow meter and as I said run very well from medium throttle onwards.

First job seems to be check physical alignment etc and then check for air leaks etc.

The only engine mods I know about ,and they wouldn't effect this problem, were the extra oil feed to the rockers, and hardened valve seats, both before I bought the car.

Wont help running but ditch the extra rocker oil feed.as they are not good

Stuart.