As I get Ole Reliable closer and closer mechanically to where I want her to be, smaller things start to annoy me. I am running the old HS6 SU Carbs and after the engine is warmed up when I come to a stop my idle stays up around 1500 rpm or sometimes higher. If I blip the throttle slipping my toe off the pedal it will usually slow the idle slightly to about 1200 rpm. However, if I shut the car off and then restart it ... it will sit there and idle happily at 800 rpm or sometimes even lower. I recently replaced the choke cables so the choke is working properly and shutting off completely. The fast idle linkage seems to be free moving ... ..there appears to be no loosness in the throttle shafts ....... anyone got any suggestions ???

Brett
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

Hi Brett;
I don't know if you have power brakes, but if so remove the hose connection and try again for the fast idle. Same with the crankcase breather. Also be sure the intake and exhaust manifold nuts to the head are secure and the gasket is good. If all is well on those items, then remove the throttle return springs and wiggle the throttle shafts as you rotate them off idle. It sounds like there must be some play. The shafts and bushings wear oval, and when the two "merge" they form different passageways unpredictably. I have about forty pounds of SU shafts and plates ready to go to the scrap metal recyclers, and ALL of it is worn beyond belief.
Someone mentioned the distributor weights, and I have found that they will hang up at times and keep the advance up so much that the idle increases. Kind of a vicious circle with some extra air coming around the throttle shafts.
Rhys

Is this a recent occurance? What was the last thing you altered or worked on?

"blipping the throttle" and "restarting" bringing the idle down sounds a lot like a sticky butterfly or over-run valve in the butterfly. If this has been happening from "day one" with this engine combo (or since the carbs were last put on) it could be a mis-aligned butterfly in the shaft or a binding interlink between the carbs (or the afore mentioned overrun valve).

The float difference is not a major concern (although you are describing H-type floats and not HS type floats) as the level of the float is adjusted with the solid type floats by altering gasket thickness under the needle valve. This can be done regardless of the cover type.

I'd also check to ensure you have proper clearance between the fast idle cam and the throttle lever. Also, try separating the carbs by loosening the interlink clamps. If this is mis-adjusted you can get one carb being forced open, even with the throttle closed on the other.

Mike!

OK hands just cleaned up .... I pulled the float bowls apart and reset the float level ... they are sealing properly ..tested by blowing with the cover upside down .... however I did find that the bowl of the front carb was almost dry while the rear was fine .... appears there is a slow leak where the line comes out of the front float bowl to the jets ... will have to get that looked after post haste ... I cleaned and lubricated all throttle and choke linkages .. have new choke cables so they slide really well ... I added two large hose clamps around the tops of the dash pots and the choke cables and just snugged them enough to make sure that the cables were not being pushed back out off their seats and therefore not shutting the choke off completely .... I got a small piece of rubber windshield washer hose and plugged it with a sawed off 3" nail and plugged the vacuum advance lead on the back carb .... Fought my home built dual carb aircleaner off and back on with minor amounts of cursing and blood letting .... now it's time to go for a test drive ...... but somehow ... I have a feeling that the old problem will still be there ..... back in a while with the final results ...

Brett
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

Well, I called it right .... OK anyone got any more ideas ?? I must admit that the throttle linkage feels much smoother ... but I do have to rethink the choke cable setup .... had to loosen them and make sure that the chokes were truly off before the test .... so it isn't the fast idle setup .... wonder if the leak in the line to the jets is causing it ..... but then why would it idle properly after startup ????

scratching my head ....

Brett
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

I really suspect that one of the throttles is not closing to the same point reliably -- not much else it could be. Why it's not, I can't tell you, but it only needs to be a teeny bit inconsistent to cause several hundred RPMs difference in idle speed.

You're probably right Phil ..... guess I'm just going to have to live with it. Just got back from a nice evening cruise, the sunset was glorious over Nova Scotia's beautiful Annapolis Valley this evening .... one just has to feel that there are many things right with the world ;-)

Brett
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

Hi Mike .... This has been an ongoing problem .... just that it has become more aggravating as all the other problems have been looked after .... as you might note, I pleaded OLD PHART's Disease on the float description .... I was remembering the one in the last carb I had apart ... the one on my lawn tractor ...

Brett

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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

As Phil alludes to, the issue may be at the butterfly connection to the throttle shaft (or the darn shaft/bush in the carb body). The best way to check the shaft is the old flammable gas/liquid squirted on the outside of the shaft and listen to the engine speed. Any change (up or down, depending on various factors) means a leak.
The butterfly can only be checked by removing the carbs and physically checking the seal when the are supposedly "closed." Also check that the overrun valves (if equipped) work OK. Not stuck, spring not missing, not too gunked up.

Sometimes the linkage between the carbs can push against the shafts and cause them to put undue lateral pressure against the butterfly and they stick or wear against the side of the carb. Loosening the interconnect levers and pulling them away from the carbs helps unless the shaft is slightly too long in which case you either have to shorten the shaft or loosen the carbs and retighten tehm to the manifold while applying pressure to the outboard to give a little more room.

Ongoing implies that there is a physical issue (misalignment) with the carb/manifold as opposed to general wear or something having broken.

Last place to look is the plugs in the manifold. They could be faulty (somehow) and allowing a leak. I recall someone who had pressed in plugs that would move as manifold vaccum increased and decreased and it couldn't be diagnosed until he actually poked at them with a screwdriver.

Mike!

You have described what I have been fighting for months. The valves have been adjusted, timing checked, even put in a rebuilt (vacuum) distributor, corrected the PCV system, new springs, no air being sucked in anywhere else that I can find and had the carbs rebuilt and throttle shafts done twice as there was a leak. After all that, what you described continues. I am waiting for replacement SU's right now and if they don't do the trick I will be lost and be forced to actually take it to a shop. When you find your solution, please post it. It will be interesting to see if we are fighting the same demon.
DC

I've got the problem with my SU's. Idles about 1400 rpm. Blip the throttle and it slows down to aprox 1000 rpm. Shut off the car, blip the throtle once again, start up, idles around 800.
Cause on my SU's: worn out throttle shafts. The throttles just don't close as nicely as they should anymore. Somehow the vacuum or the air flow also prevents the throttles to return fully. If I 'help' them a bit by pushing them back by hand it does work. Heavier return springs might do the job also, although this increases throttle shaft wear a bit more.

Cheers, Ben
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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)

Well Guys .. it's nice to know that I am not alone in this one ..... today I am going to reset the float level and clean the needle in the front carb BTW They have been replaced within the last year or so , and plug the vacuum lead on the back carb and see what happens ..... and about the description of the carb floats I gave a few postings back ...... well ummmm can I claim OLD PHART's Disease? I described the float in the last carb I had apart .... the one on my lawn tractor ... D'Oh !!

When and IF I find a cure I'll post it .... HAPPY VOLVOING !!

Brett
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

A worn distributor will cause this or a partially seized advance retard mechanism. Often it can be cured by stripping, cleaning and lubricating it. (re-assembly after that may help too)

Regards


Pete

Hi Pete ... nope not Distributer ... it's been rebuilt and fitted with CRANE XR 700 optical trigger ... but a good thought though ...

Brett
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

if it's not air it,s gas. If the needle valves are leaking in the float bowls, or the fuel pump is aftermarket and putting out so much pressure it pushes past the needle valves (how do I know!) you will get fast idle from a rich mixture. Not sure why turning it off helps though.

Hmmmm I AM getting some leakage from the front carb float bowl .... would this also cause run on too ?

Brett
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

if by run on you mean what i call "deiseling" a slightly rich carb could cause this. Deiselling is usually caused by red hot carbon deposits in the combustion chamber causing the fuel air mix to continue to ignite even after the ignition is turned off. The carbon build up can be caused by a number of different things, rich carbs, poor ignition timing, maladjusted valves, etc...oh yeah, and just plain high milage.

LOL .. HIGH MILEAGE ??? Whatever could you mean ???? The engine has just been rebuilt this summer ... .030" overbore ... new pistons .. ,Isky cam ... but it is running rich my tailpipe has not as yet turned that nice charcoal grey colour that I interpret as the result of a prober mixture ....
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

Also the way the throttle plate fits in the throat is important. It is possible to have tight shafts with no leakage but to have leakage around the actual throttle plates. They are adjustable. BTW seeing as you have overbored the engine it probaly sucks a little harder than before exagerating any leakage from before. ALso, I would tune the beast asap no point in putting undue strain on a rebuilt engine, have fun with that, patrick.

One trap for the unwary is that the design for the floats changed from SU at some point. The original floats have a metal arm kixed onto the plastic float. The replacement floats are made in one piece without any metal at all. The problem is that it changed the geometry, if you have the modern type float, you need the matching lid. New float + old lid = flooding carb.

Also check that the forks on the throttle spindles are adjusted properly, the pins on the throttle lever should be completely free in the forks at idle.


Regards


Pete

Hmmm ... Both floats are circular hollow brass rings .... but I DO remember swapping float chamber tops around a couple of years ago ... now what happened to that other top ..... well tomorrow I will pull the top off that carb and check out that needle valve ... give it a cleaning and see what happens maybe adjust the float level so it will close tighter (adjust the float to close the needle valve sooner)
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

Do you have the return springs hooked up?
How are your throttle shaft fits? Have your throttles given
you the shaft? Re-bushing is fairly easy and so is reaming for
oversize shafts in mild cases. (The shaft wears more than the body,
so an oversize shaft and reaming with a "P" reamer might save rebushing.)
Joe Curto on Long Giland has parts if they are not available at a more
accessible location. You can call him at (718) 762-7878 𖙲-SUSU]

And of course there is the ever present air leak somewhere else.
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George Downs, Bartlesville, Oklahoma, Central US

Hi George ...Return springs are heavy duty ...I have developed wonderful calf muscles on my right leg ;-) ..... throttle shafts are tight ... Have dealt with Joe Curto and undoubedley will again .... so looks like I had better start looking for that air leak ... do you suppose that the small connection on the back carb for the vacuum retard/advance being left unplugged would cause it ??

Brett
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Brett Sutherland & the 1.5 million mile 122 CANADIAN www.ecvintagevolvo.com

It could certainly be a major contributor.
Try putting your finger over it.....
A short piece of tiny hose and a nail work pretty good.
BTDT
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George Downs, Bartlesville, Oklahoma, Central US