This is probably a subject that has been covered in depth previously, so I am sorry if it is a repeat, but this is a problem that I have had with my car that I just don't seem to be able to resolve.

There is a composite spacer between the carbs and the inlet manifold made from a steel backing plate and a rubber spacer.  Its role is to allow the carbs and the manifold to be bolted together, to reduce heat flow from the engine to the carbs and to reduce the vibration that causes fuel frothing.  The latter may be marginal.

My 8v engine had a severe vibration at around 3,500 rpm.  I have ascribed this as the root cause of the problem that I have been having.  My carbs have had a habit of falling off     Usually the adhesive used to stick the rubber to the steel just peels away from the metal, but sometimes the rubber just splits.  I have just fitted a 16v engine   that has been balanced and new engine mountings, so it does not vibrate. but after only 800 miles there are signes that the carbs will fall off soon.

Things I have tried are:
Get rid of the K&N pancake filters and refit a TR7 airbox, ensure that the support on the back plate of the airbox pressing is bolted to the plate on the carb mountings for that purpose: to stop the carbs cantelevering off the spacer

Fit large jubilee clips over the inlet manifold and onto the linkage to remove some of the load from the spacer

Fit a balanced new build engine and engine mounts to minimise the vibration

This is getting expensive and I don't seem to be nearer resolving the problem, however I expect I am not the only one suffering it.  Anyone got any ideas / advice please?  

Chris

chris

i think the dolomite club do uprated ones,

cheers andy

Yes, I believe they are solid? Well worth a look on the dolly forum.

I don't know why but I have never had a problem - bet I wish I hadn't said that

Solid mounts would seem the only answer but what about this fuel frothing? Can't beleive it matters that much and if that was the case why does it only affect this engine?

Hi Martin, Please could you post a picture of your carb mountings.

Thanks very much.

Try to get original spec mounts, there are some really bad quality aftermarket items around.
Had a pair of new aftermarket mounts which sheared off within a year ...

I use a few sturdy cable ties to get the stress off ...



Also bear in mind that the original rubber support mount for the air box is very soft and allows for quite a bit of movement.

As Martin stated, these mounts are flexible to prevent fuel frothing, but also to isolate the carburettors from heat transfer from the engine.
A friend has been using the solid mounts for years without any big problems, only some very light vapour lock when weather was very hot.
But that car (Dolly 1850) was used as a standard spec daily driver ...

Hi Theo

Thanks for the picture.  You seem to have the same setup I had with my 8v engine.  I presume you put a standard airbox with K&N filter on aswell.  I used Jubilee clips instead of cable ties.

I had put the problem down to the roughness of my 8v engine, but it looks like the same problem will persist with the 16v engine, although the Sprint airbox does not have the support bracket that the TR7 airbox does on the back.

I am currently modifying my Sprint airbox to have a support bracket to stop the carbs / airbox cantilevering from the mountings and am fitting some new "old" mountings. I am not too hopeful this will be a long term cure.

I have looked at the Dolomite Club website and enquired about mounting blocks they have for sale.  I have a feeling they may be solid aluminium.  That will not help with heat transfer or frothing.

Here you go Chris as requested both 16 and 8 valve varieties!

Having read the comments in this thread though I think I'll invest in some heavy duty cable ties anyway

Quoted from Chriss

... I presume you put a standard airbox with K&N filter on aswell ...

Wrong presumption I use deep K&N filters with ram pipes on the DHC

Very nice, in fact the whole car is.

Do you have supports under them that prevent them cantilevering off the mounting blocks?

No, just the cable ties to support them.
But as soon as I run out of spare mounts I'll probably fabricate something  like the mounts used for Weber carbs.

ps. the DHC looks a bit more used after a two week holiday in Süd Tirol  

Thanks Martin is the top 16v and bottom 8v?

I have not found a way to do the cable tie trick on the 16v yet.

Quoted from Chriss

Thanks Martin is the top 16v and bottom 8v?

I have not found a way to do the cable tie trick on the 16v yet.

Yes that's right Chris

You could use the standard TR7 linkage plate and weld in a section in the middle?

I'll have a look at that when I gat the car back.  The car is a 2 Stroke to turbo (my Saab fettlers) at the moment.