24 replies to this topic

[Glun34]

Hi Everyone,

 

looking to see if anyone out there has some suggestions on a bogging down issue I'm having. It does have a turbo but the issue im having is way before the turbo is doing anything so I've put it in this section. please remove if thats not correct! 

 

Car's spec is - 

 

1275

stock head, crank and pistons.

Metro turbo T3

Stock turbo regulator

Sytec fuel pump

HIF 44 Turbo carb recently rebuilt by AC Dodd with 5w-30 dashpot oil. balance pipe blocked off and part throttle lean off connected.  

Lucas electronic 65D distributor

 

The problem I have is any sharp movement in throttle and the engine bogs down/goes lean. But if you slowly apply throttle it will rev up.

 

I went out for a drive the last time I looked at the car 2 weeks ago and recorded a video of a fuel pressure gauge i have between the carb and the regulator. its set a 3.5psi at idle but when you apply throttle quickly you can see that the pressure is dropping. I thought that must mean the pump was on the way out as the regulator is a brand new one from mini spares, so I replaced the pump with the Sytec unit and still have the problem.

 

Looking at some threads with people having similar problems, people seem to put the issue down to timing. So today I have replaced the old turbo dizzy with the 65D and set the timing to 6 degrees at 1500rpm with the vac pipe disconnected. I still have exactly the same problem, any sudden application of throttle and it bogs down and goes lean. 

 

Does anyone have any ideas? I've changed so much on the car now that im starting to think there is some other underlying issue with the engine its self despite it and the turbo having been rebuilt less than 500 miles ago!

 

Any suggestions of what to check or do are really appreciated!   

 

Cheers!

[absx2]

Other than checking the dash pot oil is still there how good is the fuel as I had a duff tank full a couple of weeks ago which within a mile gave me a lot of bogging down and mid range pinking/ pre ignition.

I had to dump the fuel into the motor bike that will run on anything and a fresh tank full not from Morrisons sorted the problem.

[cal844]

Fresh fuel, clean the electrics and then check the timing. You dont want to make any further timing or fuel ratio changes until you find the fault.

So use a known good fuel source (if you have a daily driver that is a petrol, drain some from that and top up with the fuel from the mini.)

I've also had a bit crud in the carb, not a big piece but enough to give issues

[Glun34]

Thanks for the suggestions guys. The fuel in there is a few months old, so I'll try and get a few fresh liters and see what happens. Im not sure it will make a difference for the problem im having but worth a shot! Possibly some new plugs are a good idea as well. My other thought is I've heard of certain fuel filters being able to restrict flow, so im not sure if thats part of my problem also.      

[sonscar]

I know nothing about turbo minis so this may be unhelpful.Bogging down can be too rich as well as too lean.The fuel pressure dropping should not affect the bogging unless the float chamber empties.The timing issue probably will not be solved by moving the distributor but it may be as a result of vacuum advance/retard.On a carb turbo is the float chamber referenced to the manifold?.Just some thoughts.Steve..

[Mini Manannán]

Try some lighter oil in the dash pot first.

[Cooperman]

It might be the ignition advance curve. Is the dizzy set-up for a forced induction engine?

[dyshipfakta]

Is the fuel pump meaty enough? Needs to be able to provide 3psi above boost pressure. So 10psi plus

[Turbo Phil]

Oil in the dashpot ?
Will it run under boost if you apply the throttle slowly ?

Phil.

[Glun34]

Thanks for the replies guys,

 

Although the distributor thats on there at the moment isn't turbo specific I did have a genuine metro turbo dizzy in there before and still had the same problem. That makes me think this more a fuel/air flow problem than a timing issue.

 

I think the pump has to be up to the job as its got a running pressure of 5 bar and max of 10 bar. I also know quite a few people that are running the same pump on turbo setups with no issues. I also had a genuine metro turbo pump in there before and had the same issue.

 

Theres 5w-30 in the dashpot at the moment and I have also tired 3-in-one in there as well and still have the same issue. I should also mention that I have the standard turbo BDD needle in there and also the correct turbo gasket between the carb and plenum.

 

it runs on and off boost if you apply the throttle slowly. It really doesn't seem to like to get going but once its rolling you can slowly apply the throttle until its wide open. if you were to plant the throttle or make a sudden moment it will go lean and bog down. The regulator must be working correctly as when you're on boost the afr reads around 12, so the fuel pressure must be rising with boost pressure.

 

I still haven't got a clue what it could be now as I've changed most of the items that you would think an issue like this would occur from!

 

Cheers!

[sonscar]

How do you know it is going lean?A lean AFR reading can also be a result of excessive richness.I am more familiar with EFI than carbs and distributors.Steve

[cal844]

If you've tried a 3 in one and a 5w30 it may well be you need to go heavier again. For all the time it takes it would be worth a try.

[cal844]

If you've tried a 3 in one and a 5w30 it may well be you need to go heavier again. For all the time it takes it would be worth a try.

[Turbo Phil]

I’d go heavier with the dashpot oil. To thin an oil will allow the dashpot to rise to quickly and cause a lean mixture.
Thicker oil will slow the rise and increase the Venturi effect over the jet richening the mixture.
Getting this transition from off boost into boost is the most difficult part to get right when on a boosted SU setup and is a balancing act between oil, spring and needle profile.

Phil.

[Glun34]

How do you know it is going lean?A lean AFR reading can also be a result of excessive richness.I am more familiar with EFI than carbs and distributors.Steve

 

I thought exactly the same thing! But if I pull the choke out the problem goes away. So from that I think it has to definitely be going lean, opposed to the gauge showing a lean reading from an extremely rich mixture.

 

I'll try some ticker dashpot oil and see what difference it makes. Was thinking about some 20w50. 

 

I also have another dashpot spring that isn't marked but much stiffer than the yellow one thats in there at the moment, so that also might be worth a try.

 

Cheers for the suggestions everyone!