JERKY RIDE!!

[DJF]

Can anyone help with this little problem.

 

When either decelerating or with slight accelerator pedal pressure the ride becomes jerky and lumpy. When under acceleration everythings fine.

The carbs have new needles, new plugs fitted and timing ok; could it be the mixture ?

[Dazzer]

Sounds like missing under light load, could be a miriad of things. However, TRs do have a tendency to kangaroo ever so slightly, at takeoff after slowing down and/or decelerating with your foot still resting on the pedal, its to do with the movement of the car and the sensitivity of the throttle etc. Perhaps this is what you describe?

 

Otherwise, are you still running points and condenser? If so change these first and then have a go at the mixture.

 

Dashpots off, SU or Stromberg, level the jets up to the bridge, take them down a turn and a half each and start from there.

 

Cheers

 

Darren

[DJF]

Sounds like missing under light load, could be a miriad of things. However, TRs do have a tendency to kangaroo ever so slightly, at takeoff after slowing down and/or decelerating with your foot still resting on the pedal, its to do with the movement of the car and the sensitivity of the throttle etc. Perhaps this is what you describe?

 

Otherwise, are you still running points and condenser? If so change these first and then have a go at the mixture.

 

Dashpots off, SU or Stromberg, level the jets up to the bridge, take them down a turn and a half each and start from there.

 

Cheers

 

Darren

 

Hi Darren

Thanks for the advice; I'll work through your ideas and hopefully solve the problem.

 

David

[bob-menhennett]

David

A couple of thoughts.

Correct level of oil in the dashpots ?

Is the accelerator action smooth , well lubricated, spring snapping the

carbs back to rest quickly ?

 

Bob

[graeme]

Hi David,

 

I would be looking at the carb spindles for wear. Small throttle openings correspond with the greatest wear area, hence allowing too much air via the spindle and weakening the mixture. This is assuming the carbs are set up correctly.

 

Try opening the throttle to about 2000 RPM and then waggle the end of spindle and see if the engine note alters.

 

Graeme

[DJF]

David

A couple of thoughts.

Correct level of oil in the dashpots ?

Is the accelerator action smooth , well lubricated, spring snapping the

carbs back to rest quickly ?

 

Bob

Hi Bob

 

I've not had chance to look yet at the springs although they were well lubricated within a week of purchasing the car (Oct 08); car has run OK since new needles etc; this prob has just developed.

 

I'll run through your suggestions Bob and thanks for your time.

 

David

[DJF]

Hi David,

 

I would be looking at the carb spindles for wear. Small throttle openings correspond with the greatest wear area, hence allowing too much air via the spindle and weakening the mixture. This is assuming the carbs are set up correctly.

 

Try opening the throttle to about 2000 RPM and then waggle the end of spindle and see if the engine note alters.

 

Graeme

 

 

Good point Graeme, I'll give it a try; thanks for taking the time to respond

 

David

[BrianC]

SUs or Strombergs?

If Strombergs, check the diaphragms aren't starting to perish or split (and always carry a spare set, even if the carbs have been rebuilt - must remember to get some myself )

[Badfrog]

Can anyone help with this little problem.

When either decelerating or with slight accelerator pedal pressure the ride becomes jerky and lumpy. When under acceleration everythings fine.

The carbs have new needles, new plugs fitted and timing ok; could it be the mixture ?

 

Yayyy!!!

 

A new carb thread.

If Strombergs, buy a fish tank.

Now, first, which car, which SU's, which needles.

Then, we should see this thru even if it takes everybody's tuppence on the forum.

As a prelim, if it's happening with closed carbs (decceleration), it's an air leak somewhere. But, as Darren said, it could be so many things.

 

Cheers,

Edited December 30, 2008 by Badfrog

[DJF]

Yayyy!!!

 

A new carb thread.

If Strombergs, buy a fish tank.

Now, first, which car, which SU's, which needles.

Then, we should see this thru even if it takes everybody's tuppence on the forum.

As a prelim, if it's happening with closed carbs (decceleration), it's an air leak somewhere. But, as Darren said, it could be so many things.

 

 

Hi Badfrog

 

Thanks for the reply

 

Car: TR4A

Needles: BEM (new, recently fitted)

Its not happening on closed carbs, but mainly when accelerating either after changing gear (especially in 2nd) or to maintain a constant speed i.e when in 4th. Need to dip clutch and then increase the revs to smooth out the jerk

 

Cheers

David

[Badfrog]

Car: TR4A

Needles: BEM (new, recently fitted)

Its not happening on closed carbs, but mainly when accelerating either after changing gear (especially in 2nd) or to maintain a constant speed i.e when in 4th. Need to dip clutch and then increase the revs to smooth out the jerk

Cheers

David

 

Hi David,

 

How come you have such weird needles? I think they're floating needles and should not belong to a honest 4A.

In any case they're new and as such, would make good culprits if needle installation and jerky ride coincided.

 

Are you sure we're talking SU's ? What is exactly your carb model? If H6 or HS6, put back a classic set of needles on if you still have them (TW, SM, TS, RH, from lean to rich, SM is average)

The BEM needle is a very very lean needle. I don't have my SU books now, but I'll check what car it is supposed to go with tomorrow.

 

Cheers,

[graeme]

Needles: BEM (new, recently fitted)

 

David,

 

I suspect that you may have later SU HIF44 carbs fitted with BEM needles. These should be good carbs on the TR4A but will need setting up correctly and as Badfrog says, these needles are too lean for the TR. That's probably were your problem lies.

 

This is a good site for checking needle profiles.

 

http://www.mintylamb.co.uk/suneedle/

 

 

Cheers

Graeme

Edited December 31, 2008 by graeme

[Badfrog]

David,

I suspect that you may have later SU HIF44 carbs fitted with BEM needles.

These should be good carbs on the TR4A but will need setting up correctly and as Badfrog says, these needles are too lean for the TR.

That's probably were your problem lies.

This is a good site for checking needle profiles.

http://www.mintylamb.co.uk/suneedle/

Cheers

Graeme

 

David,

 

I agree with Graeme, the Minty Lamb site is great. I use it on a regular basis for simple checks.

The WinSU software is great when you want to get a bit more technical.

( http://www.winsu.co.uk/ )

 

Back to your car, HIF44s are essentially Volvo B20 carbs and they never were original carbs on TRs. Some suppliers offer a good-looking 3 HIF44 combo for six cylinders TRs. I don't have any experience on how they perform.

 

Nevertheless, they are 1.75" SU's and this makes them equivalent to HS6. Of course, the car has been tweaked so you don't know how your carbs are set: 0.090" or 0.100" jets? Normally, HIF's have 0.100" jets. You definitely want these.

 

A reasonable equivalent to the fixed SM spec among 0.100" floating needles would be BAF, BAL or BAA (BAF seeming the best possible).

This being said, I have tried to set floating needles in HS6 SU's (using Volvo 144S HS6 pistons). These floating needles are longer than the fixed ones and generally perform poorly in TRs at high revs.

 

In conclusion, your needles are way too lean and you have three choices, starting by simplest:

 

1) try BAF, BAL, BAA needles (make sure you have 0.100 jets)

2) find fixed needle pistons adaptable in HIF44's dashpots and use SM needles.

3) Get HS6 carbs with SM needles and eBay out your HIF's.

 

Don't you love SU's?

 

Cheers,

Edited December 31, 2008 by Badfrog

[DJF]

David,

 

I suspect that you may have later SU HIF44 carbs fitted with BEM needles. These should be good carbs on the TR4A but will need setting up correctly and as Badfrog says, these needles are too lean for the TR. That's probably were your problem lies.

 

This is a good site for checking needle profiles.

 

http://www.mintylamb.co.uk/suneedle/

 

 

Cheers

Graeme

 

 

Hi Graeme

 

Thanks for the info and advice; this Forum is just so useful. Experienced TR people like yourself and everyone else who has replied to my question are invaluable to novices like myself having only owned a TR since October and still finding my way around.

 

Another question to you and Badfrog!!

 

I need to replace the gear shift gaiter - I've removed the bolts securing the fascia support bracket to the floor and dash but cannot release the bracket to enable the housing to be lifted over the gear shift lever - am I missing something!!!

 

Cheers and Happy New Year

 

 

David

[DJF]

David,

 

I agree with Graeme, the Minty Lamb site is great. I use it on a regular basis for simple checks.

The WinSU software is great when you want to get a bit more technical.

( http://www.winsu.co.uk/ )

 

Back to your car, HIF44s are essentially Volvo B20 carbs and they never were original carbs on TRs. Some suppliers offer a good-looking 3 HIF44 combo for six cylinders TRs. I don't have any experience on how they perform.

 

Nevertheless, they are 1.75" SU's and this makes them equivalent to HS6. Of course, the car has been tweaked so you don't know how your carbs are set: 0.090" or 0.100" jets? Normally, HIF's have 0.100" jets. You definitely want these.

 

A reasonable equivalent to the fixed SM spec among 0.100" floating needles would be BAF, BAL or BAA (BAF seeming the best possible).

This being said, I have tried to set floating needles in HS6 SU's (using Volvo 144S HS6 pistons). These floating needles are longer than the fixed ones and generally perform poorly in TRs at high revs.

 

In conclusion, your needles are way too lean and you have three choices, starting by simplest:

 

1) try BAF, BAL, BAA needles (make sure you have 0.100 jets)

2) find fixed needle pistons adaptable in HIF44's dashpots and use SM needles.

3) Get HS6 carbs with SM needles and eBay out your HIF's.

 

Don't you love SU's?

 

Cheers,

 

 

Hi Badfrog

 

Thanks for the advice; I think I'll try Option 1, having checked the jets first.

 

As I mentioned to Graeme, the Forum is a great asset for TR novices like myself. Once again many thanks.

 

Cheers and Happy New year

 

David

[graeme]

David,

 

Happy New Year to you.

 

With regard to the H frame which connects between the floor and dash, this is usually very tight and I use a screw jack, suitably protected, between the floor and underside of dash in the passenger footwell. It doesn't require much movement, about 1/4 inch should relieve the pressure holding the H frame in place.

 

Best of luck

 

Graeme

[Badfrog]

David,

Happy New Year to you.

With regard to the H frame which connects between the floor and dash, this is usually very tight and I use a screw jack, suitably protected, between the floor and underside of dash in the passenger footwell. It doesn't require much movement, about 1/4 inch should relieve the pressure holding the H frame in place.

Best of luck

Graeme

 

Graeme,

 

I love your motto " If it ain't broke, fix it till it is!!". Story of my life with Lady Ann.

 

It's true that dismantling the H frame in a TR4 requires a hefty upwards push, and with a 4A where the H frame goes around the gear lever/gaiter ensemble , it's even worse.

The funniest part is reinstalling the bl***y thing and finding out the nuts and bolts got loose 10 years ago. And now the whole fascia is misaligned with the floor panel captive bolts . Hilarious when you're NOT the guy doing it.

 

Cheers,

[67_gt6]

copper/hide hammer is good for manoeuvering the H frame around

[DJF]

copper/hide hammer is good for manoeuvering the H frame around

 

 

Good idea - I'll give it a try.

 

Cheers David