Solex Carbs

[chris_seven]

I have a modified early engine running on Solexes and seem to suffer with all the ususal problems of extremely poor pick up and fuel consumption.

We have carefully rebuilt the carbs with little or no improvement and I have just bought a pair of 40IDAs in good condition.

I would, however, prefer to stick with the Solexes if possible.

I see that there is a company in Holland (Duel Motorsport) offering to rebuild/modify Solexes.

Their website claims that when modified the Solex performs very well and gives improved low end performance compared to the Weber and that fuel economy is restored.

As we use these carbs on a Rally car, I am more concerned with performance than economy but I am interested.

I contacted Duel and they gave me a price or $2000 for the mods/rebuild but no detailed information.

I do understand that this may be commercially confidential but for $2600 I can buy PMOs.

Does anyone have any information about detailed mods etc that will improve and solve the standard problems of Solex carbs?

I am not unwilling to pay Duel to do the work but I need confidence that it will be money well spent.

Any comments gratefully received.

[preS]

Hello Chris 7

I have a friend who is racing w/ Solex carbs overhauled by Duel and is extremely pleased. A few notes:

1. My friend is obligated to race his 65 w/ solex under FIA rules
2. his 65 rally car is running on Webers ..

Can you explain why you want to run on Solex for a rally car? Also why do you consider PMO when you already have IDS?

Regards,

Richard

[chris_seven]

304678

Thanks for the reply.

Our car was first registered in early 1966 but was built in 1965 and currently has FIA Historic Papers.

We generally want to run the car in the UK on BHRC Rallies but it would be useful if we could maintain the cars FIA status as I feel that will help to maintain its originality and hence residual value and also allow us to compete in Europe in the future.

We have purchased 40IDA carbs rather than the IDS as I have been advised by several people that the IDS vacuum enrichment system can be unreliable on competition cars and does tend to be tempremental.

We have no experience with the IDS so am am not speaking with any personal knowledge.

I have considered fitting PMOs because we have fitted them to a few 3.0litre engines with great success and if we move away from Solexes we have already lost the FIA status of the car and I understand PMOs generally offer improved low end performance compared to the Weber.

It would be realtively easy to resell the Webers to fund the purchase of PMOs and I would be confident that we would obtain the performance that we are seeking.

Also the design principal of the Solex seems quite good and I am frustrated that we cannot make them work correctly and I am inclined to presevere.

We are looking to build an engine with 190-200 BHP if possible and have all of the components that we need and our final decision is about carbs.

I want to set our new engine up on a dyno and don't really want to spend $2000 on carbs that then cause problems.

I can make suitable venturies of differing diameter but I am concerned that we will not be able to find suitable jets.

I hope this explains the dilemma.

[preS]

Hi Chris,

The way I look at your situation is that you ask them (Duel) if overhauled Solex will be as good as a set of PMO's. If it's never going to be that way, you have to decide whether you care about FIA or performance.

Earlier this year we did an European FIA championship rally in the 65 (finished 2nd) and we had no problems running w/ webers IDA.

Keep us posted.

Richard

[sithot]

Tony A-Z used them in the Daytona class winning 911 in '69. They had more "on top" than Webers.

Tom

[304065]

The function of the IDS weber's additional enrichment circuit is to allow you to correctly tune the high rpm range for the proper mixture. In the IDA, the lack of a high-rpm enrichment requires you the midrange adjustment to be too rich for optimum power. It is this tuning capability, not "safety" that makes the IDS more desirable for racing.

That being said, use the Solexes to preserve originality. One who knows how to properly setup and tune them makes an MFI expert look commonplace.

[preS]

Since Chris is planning on installing a Twin plug and apparently originality is not an issue anymore, should he go for Solex or Weber? And if Weber, IDA or IDS?

Regards,

Richard

[chris_seven]

304678,

We do have an engine that we are planning to Twin Plug which we plan to use mainly on Asphalt and run as a 911R Replica. I have more or less decided to run this car on PMOs as our eligibility scrutineer (BHRC) has accepted them for use on 3.0 litre engines. We will install this engine in our other car which was registered in 1967.

The question for this car is whether to use a 40IDA or a 46IDA as the original 906 engined cars used.

I guess we will have to try both and decide.

The other car that we have (1966 registered, 1965 build) will be used on gravel and we probably don't have the budget to build both with Twin Plugs.

It is this car that we are thinking about keeping on Solexes as it won't be fitted with the 911R Replica panels and maybe keeping its FIA status intact is a good idea.

I am interested to understand the IDS enrichment circuit as three or four engine builders in the UK have told me to either avoid these carbs or modify them to remove this capability, effectively changing them to an IDA/IDT.

I can probably find a pair of new 40IDS carbs but the asking price is around $3250.

With regard to performance gravel rally cars don't spend too much time at peak rpm and mid range is more important than in a typical race car.

The reason for considering the Solex modified by Duel is the claim that the mid range is better than with the Weber as the top end performance of our existing single plug engine is quite good, it the the catastrophic flat spot at around 3000rpm that is the killer.

I guess we probably have our engine strategy back to front. I guess we should use Twin Plug for gravel and single plug for asphalt but we don't want all the stone damage on the 'R' replica.

[Grady Clay]

Chris,

There are two issues that are peculiar to Solex; first is that the floats
tend to absorb fuel and sink. The “fix” is to have several sets with the
extras drying out. Weighing the floats will tell.

The other issue is with fuel boiling in the circulation circuit. It is possible
to hide a fuel “cool can” full of ice behind the air cleaner assembly and
circulate the fuel through it and back to the chambers via the fuel feed
to the overflow tube. This works well for track use where you can
replenish the ice every session. Having very cold fuel from the fuel
tank helps but doesn’t solve the problem.

You can test to see if this is a problem by measuring the temperature
of the fuel in the float chamber (reservoir). If the fuel gets into the
80F+ range there may be a problem. Another test is to vent the float
chamber (reservoir) not to the air filter assembly. It always is a good
idea to vent the two float chambers and the six overflow chambers to
a catch tank and then overboard. Fumes from those will cause the
engine to be rich when the fuel is hot.
"
Attachment 20737"
(C) Dr. Ing. h.c. F. Porsche K.G.

To make this work, exchange the single banjo at #3 and #6 with the
double banjo at #1 and #4. Extend the hose that used to connect
at #1 and #4 to the coils in the bottom of the “cool can” (red).
The return from the “cool can” now connect at #3 and #6 (blue).
Have two separate coils in the bottom of the can. The “cool can”
can perch atop the shock cross-member. You can make it where it
fills with ice behind #3. Put a drain about 1/3 up the can and drain
it to the inlet side of the cooling fan. Make the can as big as practical,
insulate it and paint it flat black. A modified Sportomatic vacuum
reserve tank would work well. An oil fill neck and cap would work
well.


Otherwise the problems are similar to Weber – worn throttle shafts,
dirt and corrosion, mis-treatment over the years, etc.

Best,
Grady

[preS]

Hi Grady,

Nice reply. Thanks.

Re. DuEL and solex rebuild. I have an Austrian friend who races a 65 that is fully prepared by DuEL. From what I have learned is that DuEL does not just rebuild Solex but also improves them which apparently cures the problem that they came w/ from the factory. In 4 years of FIA racing my friend never had a carb problem and he wins his class (C) most of the time. Later this month, June 23-24, they will be racing on the Nurburgring in Germany for the 3 hour endurance race (for those living nearby and might want to gather more information).

Not affiliated, etc.

Richard