Alfa Romeo Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter #1
Hi there - my '68 1750 spider with twin Weber DCOEs pops on to three cylinders when on part throttle. Put your foot down and all cylinders chime in no problem, but part-throttle driving is a problem - for example, exiting a side road, or running through town. At idle, and running on three, I disconnected each plug lead in turn and found that it seems to be number 3 that cuts out. I've just had new plugs, leads, distributor top and condenser fitted but suggest it could be a fuel problem? Maybe accelerator pump issue? Could the rubber carb mounts be at fault? I've just resurrected the car from its winter hibernation and it started up no problem, but on the first drive out it suddenly started running rough. Any words of wisdom much appreciated! Thanks in advance! Paul
 

·
Registered
Joined
·
2,370 Posts
Was the fault there before you had new lead and plugs? It wouldn't be the first time I have seen a new component that is defective. I would try the following:-

1) Swap the plug from 3 to 2 and see if the fault follows the plug.
2) Swap No. 3 and No 2 plug leads (both ends obviously) and see if the fault follows the lead.
3) Spray some WD40 or other penetrating oil around the carb rubbers. If there is a leak the penetrating oil will enter and change the engine note.
4) Put your old distributor cap back on.
5) Just to rule it out I would do a compression test.

Personally though it sounds like dirt in the carbs and a strip and clean is going to be required.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #3
That's great advice - many thanks. My Sunday will be spent under the bonnet...! I suspect the carbs need a good clean in any case but troubleshooting the ignition system is a great start. Do you have any good experiences with carb cleaners and can you recommend one?

I'm reasonably confident it's not a compression issue as they were checked last year - all OK. Thanks again - Paul
 

·
Registered
Joined
·
3,537 Posts
That's great advice - many thanks. My Sunday will be spent under the bonnet...! I suspect the carbs need a good clean in any case but troubleshooting the ignition system is a great start. Do you have any good experiences with carb cleaners and can you recommend one?

I'm reasonably confident it's not a compression issue as they were checked last year - all OK. Thanks again - Paul
I'd go with the carbs as being at fault if kands idea doesn't indicate ignition problem - buy a service kit before you strip the carbs but start by taking the jets out and blow through with an airline if you have access to one then give another go before you go the complete strip down route
Unlikely to be a pump problem if its only doing it on part throttle as the pump comes into action on throttle movements rather than feathering, also have you checked the mixture on the carbs, worth doing as its very easy and has an impact on part throttle
 

·
Registered
Joined
·
146 Posts
My 1750 used to sometimes fouls its number 3 plug too!

Everything above is what I did to solve the issue, it turned out that the carb was over-fuelling that cylinder, so once I reset them it was fine.

Good luck.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #6 (Edited)
All done and sorted - great advice thanks everyone. I took all the jets out, blew them through, took of the carb tops and cleaned out the bowls, checked the float levels etc. Then checked all the ignition parts once again. Not quite sure what was at fault but it runs great again now. What kind of a job is replacement of the rubber carb mounts as I noticed some signs of perishing?

Thanks one and all!

Cheers

Paul
 

·
Registered
Joined
·
10 Posts
Discussion Starter #7 (Edited)
My 1750 used to sometimes fouls its number 3 plug too!

Everything above is what I did to solve the issue, it turned out that the carb was over-fuelling that cylinder, so once I reset them it was fine.

Good luck.
All done and sorted - great advice thanks everyone. I took all the jets out, blew them through, took of the carb tops and cleaned out the bowls, checked the float levels etc. Then checked all the ignition parts once again. Not quite sure what was at fault but it runs great again now. What kind of a job is replacement of the rubber carb mounts as I noticed some signs of perishing?

Thanks one and all!

Cheers

Paul
 

·
Registered
Joined
·
146 Posts
All done and sorted - great advice thanks everyone. I took all the jets out, blew them through, took of the carb tops and cleaned out the bowls, checked the float levels etc. Then checked all the ignition parts once again. Not quite sure what was at fault but it runs great again now. What kind of a job is replacement of the rubber carb mounts as I noticed some signs of perishing?

Thanks one and all!

Cheers

Paul

Good work!

Replacing the rubber mounts is pretty easy, getting the carbs off is the hardest part. Just don't forget you need a gasket for both sides of each mount, so 8 all in.
 

·
Registered
Joined
·
3,537 Posts
All done and sorted - great advice thanks everyone. I took all the jets out, blew them through, took of the carb tops and cleaned out the bowls, checked the float levels etc. Then checked all the ignition parts once again. Not quite sure what was at fault but it runs great again now. What kind of a job is replacement of the rubber carb mounts as I noticed some signs of perishing?

Thanks one and all!

Cheers

Paul
Good work - nice intro to the satisfaction of working on these old cars - removing the carbs isn't difficult but is fiddly - I've done a H2 if you PM me your addy for a copy
 

·
Registered
Joined
·
1,106 Posts
If replacing pay a little extra and get the billet versions...


All done and sorted - great advice thanks everyone. I took all the jets out, blew them through, took of the carb tops and cleaned out the bowls, checked the float levels etc. Then checked all the ignition parts once again. Not quite sure what was at fault but it runs great again now. What kind of a job is replacement of the rubber carb mounts as I noticed some signs of perishing?

Thanks one and all!

Cheers

Paul
 

·
Registered
2017 Guila 2.0 Tbi Lusso spec, 1972 S2 Spider Junior, wife drives 939 Spider, + Abarth 595
Joined
·
6,576 Posts
Good work!

Replacing the rubber mounts is pretty easy, getting the carbs off is the hardest part. Just don't forget you need a gasket for both sides of each mount, so 8 all in.
You will also need an inlet manifold gasket.
 

·
Registered
Joined
·
146 Posts
You will also need an inlet manifold gasket.
On my GTV the inlet manifold gasket is between the manifold and block, not carb mounts and manifold... There is an identical gasket at each end of the individual carb mounts, hence needing 8 of them. If this not correct?
 

·
Registered
2017 Guila 2.0 Tbi Lusso spec, 1972 S2 Spider Junior, wife drives 939 Spider, + Abarth 595
Joined
·
6,576 Posts
Yes, you need the 8 (or is is 4 Siamesed?) but you will need to take the inlet manifold off to change the carb mounts so you will need the manifold to block gasket to.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #14
Yes, you need the 8 (or is is 4 Siamesed?) but you will need to take the inlet manifold off to change the carb mounts so you will need the manifold to block gasket to.
Thanks again, although I have heard the billet aluminium carb mounts can cause the carbs to vibrate and the fuel to froth in the bowls and interfere with the mixture. Does anyone know if there is any truth in that? It's the reason the originals are made of rubber apparently...
 

·
Registered
Joined
·
3,537 Posts
Thanks again, although I have heard the billet aluminium carb mounts can cause the carbs to vibrate and the fuel to froth in the bowls and interfere with the mixture. Does anyone know if there is any truth in that? It's the reason the originals are made of rubber apparently...
I have the Alfaholics manifold with the rubber O rings and cossie washers and can confirm that apart from being a bit of a faff when you refit the carbs it doesn't cause any problems.
 

·
Registered
Joined
·
4,053 Posts
personally don't see the need for alu carb runners on the daily driver!
Alfa weren't exactly idiots when they designed this set up (although they were idiots when it came to the heater placement!;))
The rubber inlets used with the carb stay are perfectly fine. But that is often the problem, many get rid of the original airbox to fit foam or mesh bits and bobs and chuck the stay out with it....hey presto your rubber intakes take the strain and the carbs bounce about like two wobbly puddings on a plate:)
 

·
Registered
Joined
·
381 Posts
Thanks again, although I have heard the billet aluminium carb mounts can cause the carbs to vibrate and the fuel to froth in the bowls and interfere with the mixture. Does anyone know if there is any truth in that? It's the reason the originals are made of rubber apparently...
There's absolutely no truth in this whatsoever. You use either the older type thackeray spiral washers, or the later type Cosworth style mounts, which are a pair of cupped washers and a rubber bobbin per mounting stud.
You must be careful not to tighten either of this type of mount right up. Leave a minimum of 20thou between either the coils of the spiralwashers, or between the cupped washers.
This provides the flexibility to stop the fuel frothing.

In my opinion aluminium mounts are a great step forward. The rubber mounts supplied today are very poor quality, I've seen sets of these go west in 18mths.
The aluminium mounts are "fit correctly and forget".
Think about it, just about the only companies that used rubber mounts on cars with sidedraught carbs fitted as original equipment were Alfa and Lancia.
I've owned plenty of both and believe me they are always a pain.
Almost all other manufacturers used thackeray washers in the day, Lotus, Rootes Group (Avenger Tiger, Hunter GLS), Vauxhall (Chevette HS), Ford in their RS kits, Jensen Healey, BMC Special Tuning Department with their DCOE kits for Mini's, MGB's, Healey 3000's, and many more.
Go to any Historic race meeting paddock and look under the bonnet of any make of saloon or sports car with sidedraughts fitted, no rubber mounts.
I'm an absolute Alfa and Lancia fan, but this application was one of few areas where they made a big mistake.
I've now fitted ally mounts to all 4 of my Alfa's, to great effect in each instance.

Steve
 
1 - 18 of 18 Posts
Top