Help! No power after carb rebuild.

[BenzBoy]

I've just been trying to get the Bond running right and I'm stumped.

It's a 1600 straight six with twin Stromberg CD150 carbs. I've rebuilt them and set them up as per the factory settings, synchronised the throttles, and I then fine-tuned them with a Colourtune kit. The pistons move freely and hit the bridges with a nice "clunk" so the jets are centralised.

As soon as I set off the car bogged down and ran really badly, not firing on all six and totally lacking power. I managed to get it started again and had to put a little choke on just to get it to stay running (engine was well warm as I'd just been tuning it).
I live on a hill and had to keep the revs over 3k and just feather the clutch just the get the sodding thing back up and on the driveway. Can't have done my clutch much good but it was that or abandon it at the bottom of the hill.

I've not touched the cam or ignition timing, leads are in good nick and it seems to run ok when stood still, although I have to set tickover at about 1200 rpm.

Anyone have any pointers? I'm stuck.

[scaryoldcortina]

Air leak? If you took the carbs off, are the gaskets seating properly?

[mikemai47]

Too weak under load? are float levels too high? I've had it before with all types of carb, sets up fine stationary but too weak when you need the power, apart from that did you check vac pipes?

[jrevillug]

Could it be that the diaphragms aren't seated properly? They are quite fiddly to get right, AFAIK. Or maybe the slot that allows air to the underside of the diaphragm is blocked. Either would mean that the pistons wouldn't rise, strangling the engine.

[BenzBoy]

Thanks for the advice. I've been out an re-tightened the carbs-to-manifold bolts, and checked the vac pipe connection but it's still running like poo. If I rev the engine it'll sometimes drop a couple of cylinders (hard to tell how many), and it did that whilst the colourtune was hooked up to No4 cylinder (spark but no flame) so it points to the rear carb.
It'll spit back through both carbs whilst it's running like curse word.

When I rebuilt the carbs I set the float level as per instructions so I don't reckon it's that.

The pistons seem to be rising as normal however the rear carb does lose dashpot oil far quicker than the front one. I'll check the diaphragms etc.

It's difficult because the car has never run totally right. It might be worth checking the compression on this tired engine. I compression is down then I could tweak it forever and a day and never get it going! ;D

I do have a Mercedes V8 kicking about not doing much at the moment...

[retrowagen1234]

for the symptoms you said, Id say underfueling... I had it with my bready when the float jammed up on a supposed superior webber.... Ended up doing the same thing (loads of revs and feather the clutch) to get it off a very busy main road at night....

[kapri]

Split diaphragm on the rear carb ? I know it WAS new, check it out again ?

[BenzBoy]

Right, I did a compression check and pressures read between 138psi and 150psi. I had to do it on a fairly cold engine as it won't run very well at the moment but that all seems OK to me.

I took the dashpot tops off and checked that the diaphragms are seated correctly and they are. Whether a diaphragms is dodgy... I don't know. I'll have another look tomorrow.

I'll need to centralise the jets again now that I've had it apart.

One thing I noticed is the jet adjuster on the rear carb is really stiff to turn. I've put all new O-rings in and I find it odd that one is fairly free and the other ain't. Either way I get no fuel leaking fom either.

I've got an awful feeling I'm going to have to take the carbs off again to have a proper look over them.

I'm going to give it one more go tomorrow and then see where to go from there. I do get the sinking feeling that something just isn't right with one of the carbs though.

Thanks again for all the suggestions and advice.

[Deleted]

If there was an air leak it would idle very fast and you'd have trouble getting the speed back down. It would also spit and pop just off idle, depending how bad the air leak was.

If it was Webers I'd say you've blocked a jet. If you can get it to run by pushing the throttle or using the choke circuit then you're forcing fuel in through the choke and the throttle pump, so the main jet must be blocked.

However, it's not Webers and I don't understand Stombies or SUs, so that's as far as my help can go.

Is the pot thing inside completely free to move up and down? It's not catching in the bottom is it? Where the jet drops all the way down, it can get stuck if the bottom of the carb has got bent through being dropped etc.

[lizardking]

As you say it's never run right was it running like this before you rebuilt the carbs Dean,Is fuel getting to the carbs ok from the tank?
It's been stood a while has rust built up around the pipe inside the tank?
Is the fuel filter clean?
Can you swap the front and rear carb see if the problem moves with it?
My advice is go back to basics and think logically,you need the right amount of fuel,fired at the right time,then it's just suck,squeeze,bang, blow.
An easy way to check for air leaks is to get a can of easy start or something equally volatile and carefully spray it around the joints in the fuel system,when you find where it's sucking air the revs will rise.
Strombergs are notorious for bad diaphrams and as said before they can tear if not fitted very carefully.
As a rule of thumb (NOT TRUE IN EVERY CASE I KNOW) low rev misfires will suggest fuel issues and high rev misfires will suggest timing,points etc.
That said it would do you no harm to clean your points and swap out your condensor whilst checking for track marks in the cap,worn carbon bush,loose leads,
You can usually see the condition of your leads by running the car in the dark and watching the leads for "corona" arcing-you would see faint blue sparks or something not dissimilar to the lightshow in a plasma ball running around the leads if they are in poor condition.
Just because something is new or looks ok does not mean it's guaranteed serviceable i.e a pinhole in your diaphram would cause issues (hold it up to a strong light stretch it and look through it)
As a last point are you sure your spindles are air tight because from your description both now and a few months ago I suggest you may be still dealing with the problem you had before the carb rebuild.

apologies for the essay but I want to see you happy again

[BenzBoy]

Yea the pistons moved freely, and from what I could see (when I wasn't getting a face full of hydrocarbons) the pistons were at the same level at the same rpm. If the pistons stick it's usually due to the jet not being centralised and binding on the needle. They do that now, but that's cos I've had them apart again... ;D

[BenzBoy]

Sept 11, 2010 18:14:25 GMT lizardking said:

As you say it's never run right was it running like this before you rebuilt the carbs Dean,Is fuel getting to the carbs ok from the tank?
It's been stood a while has rust built up around the pipe inside the tank?
Is the fuel filter clean?
Can you swap the front and rear carb see if the problem moves with it?
My advice is go back to basics and think logically,you need the right amount of fuel,fired at the right time,then it's just suck,squeeze,bang, blow.
An easy way to check for air leaks is to get a can of easy start or something equally volatile and carefully spray it around the joints in the fuel system,when you find where it's sucking air the revs will rise.
Strombergs are notorious for bad diaphrams and as said before they can tear if not fitted very carefully.
As a rule of thumb (NOT TRUE IN EVERY CASE I KNOW) low rev misfires will suggest fuel issues and high rev misfires will suggest timing,points etc.
That said it would do you no harm to clean your points and swap out your condensor whilst checking for track marks in the cap,worn carbon bush,loose leads,
You can usually see the condition of your leads by running the car in the dark and watching the leads for "corona" arcing-you would see faint blue sparks or something not dissimilar to the lightshow in a plasma ball running around the leads if they are in poor condition.
Just because something is new or looks ok does not mean it's guaranteed serviceable I.e a pinhole in your diaphram would cause issues (hold it up to a strong light stretch it and look through it)
As a last point are you sure your spindles are air tight because from your description both now and a few months ago I suggest you may be still dealing with the problem you had before the carb rebuild.

apologies for the essay but I want to see you happy again

Thanks Alex, it does seem like the same old set of problems doesn't it?
The tank has been emptied and cleaned, and it has complete new fuel line front to back, and new fuel filter.
Can't swap the carbs over as they are handed, but I'm still not 100% sure it's down to just one carb.
I'll go back to basics like you said and check everything out. It could well be that I still have air getting in past the spindles... I'll do a spray-flammable-stuff-test on them.
A lot of the ignition components are new but as you say, that doesn't always guarantee they work! ;D

[scaryoldcortina]

mm, here's a quick thought, how do the fuel pipes to the carbs run? Does it feed the front carb first, then a pipe to the back one, or a centre feed to both at once? I'm thinking that if the fuel flow is too low (as suggested) then the front carb might be filling up first (and running fine) but there is not enough left to fill the rear carb except at idle.

[BenzBoy]

If I remember it right, there's a T-piece after the fuel filter. It's possible that the fuel pump is a bit lazy and isn't putting enough fuel through.
The fuel filter isn't always full, but I've seen other cars like that and assumed that's normal? I can see fuel flowing through it but not at a great rate.

The rear carb is the one I had to do the repair on as the float pivot had broke, but if that had fallen off I'd have an overflowing situation I'd have thought. It's something I need to inspect, although I expect the epoxy repair to be fine.

It's frustrating, but this is the last problem I need to solve (until the next one!) so I'm kind of happy I can concentrate on just this.

*Edit* the concensus seems to be that it's a fuel starvation issue, which is something I'll keep in mind - my instinct was to blame too much fuel but with me having to give it a little choke to get it running anywhere near right, it points to too little fuel.

I shall attack it with fresh vigour tomorrow. Thanks again!

[Bob the Fish]

Is it on points? Could try a new condenser. Or points closed up maybe. It'd have to be quite a big air leak to run that badly, if it is that.

[ChasR]

New ignition systems can be a world of pain. For me (so far) the Unipart ignition parts haven't been too bad (but I don't trust their rotor arms) with Intermotor bits being very much a lottery (Rob here will tell you about how his Dolly never ran right with Intermotor parts (read backfiring via the carbs/exhaust, and unable to drive it with a severe lack of power).

Do you have access to another set of trusted ignition components?

If it's not that, I'd check the carbs. I'm not sure if Strombergs are like SUs but are the dashpots matched to the pistons (simple to check)?

[Kyle67]

If all the factory pipework is in place, it feeds the front carb first. All the 2ltr Equipes I've had have all had fuel pump/poor running issues that I've cured with the addition of an SU electric pump. May be worth a beg/borrow/steal to give one a try.
Interesting to note the comment about the spindles, I had a Sherpa Coupe come in that wouldn't tune right, lost power under load and spat it's load out of the carb. That was the often overlooked carb spindle bushes worn and letting in air. Proper rebuild kit and it was a different car.

[BenzBoy]

You know, I'm beginning to suspect the fuel pump now. I took out the gauze to clean it some time back, but when I'm manually pumping it using the priming lever I don't get a lot of fuel flow, and the clear filter is never full of fuel although I can see a small trickle of fuel running through it when the engine's ticking over. Perhaps it has a pinhole / tear in the diaphragm.

As far as I know, the pistons are matched to the bodies on Strombergs but it's not as critical as the seal is formed by the diaphragm rather than the small tolerance on SU's. Either way, when I rebuilt the carbs I did them one at a time and was very careful.

Does anyone know if the fuel filter should always be full in normal conditions? I would expect that when the carbs are full, the closed float needle jets would cause the filter and lines to fill up? This doesn't seem to happen on my car.

[Deleted]

Mine is always full.

Take it apart and give it a clean. You might find one of the valves isn't closing properly or the diaphragm is stretched.

Easy test is take the fuel line off the carb and try and blow the fuel back into the tank. If you can then the valve is probably the problem. Then turn the engine over and you should get strong gushes of fuel pump out. If not, it's probably the diaphragm.

[Kyle67]

Should be full or about 5mm from top at the most.
I'd give some serious thought to upgrading it to an electric pump, my Equipes ran much better on them as did my Dolly Sprint and VX490. The one on the Sprint was a teeny little thing but happily coped with 2 x HS8 carbs.