Carb revs higher than normal

french driver · Post by **french driver** » Wed Sep 02, 2009 11:20 am

Hi BX19 with a solex carb is showing 1500rpm and the engine is runnng fast. Adjusting the idle screw makes no differance, Engine is warm after a long drive so not cold engine.

Any ideas?

DLM · Post by **DLM** » Wed Sep 02, 2009 12:14 pm

Someone elsewhere reported raised and rising revs recently on a carb-fed BX19 in higher ambient temperature as the engine got hotter. I can't remember the exact outcome, but there was a possibility that fuel vapourisation within the carb at higher-than-usual temperatures was causing the problem.

In this case the rising revs could be temporarily alleviated by opening the bonnet for a while. From what you say this doesn't seem to be happening. Is it just raised revs at idle, or across the board, and is the throttle pedal firmly back with its stop hard up against the pedal box?

Put another way, is the throttle pedal returning promptly and fully to rest as it should do?

french driver · Post by **french driver** » Wed Sep 02, 2009 7:41 pm

The throttle is behaving normally just the revs staying just under the 1500rpm position.
Adjusting idle screw no differance unless you screw in the idle screw which in turn increases the revs further. No effect then.
Was thinking the auto choke stuck if so how can you tell?
Thanks in advance.

DLM · Post by **DLM** » Thu Sep 03, 2009 10:08 am

How about the smell of rich mixture at the exhaust - and general sooting-up at that end too?

From memory, the autochoke control is by waxstat linked to coolant temperature, and the branch of the coolant system for this is at the highest point of the coolant system, making it prone to airlock, low-coolant level problems etc. Apart from that there's the distinct possibility that the waxstat's just got too old to function properly.

citronut · Post by **citronut** » Fri Sep 04, 2009 8:08 am

i agree with DLM
but also the coolant in and out posts which the two coolant feed pipes attatch to are cast alloy, which close up due to corrosion internally,

it is possible to dismantel the wax stat housing and clean the two spouts/ports out,

the only other thing is if it were over chokeing it would also be difficult to start whilst the engine is hot,

i would give all the carb linkage's a good soaking with duckoil (contect) then move/work all the linkages,

i do NOTadvise the use of WD40 as this dry's thing out and is abbrasive

regards malcolm

charlie · Post by **charlie** » Fri Sep 04, 2009 9:55 pm

hmmmmmm

i posted about the same on the bx project

but mine's been converted to a manual choke

engine gets hot and idle revs climb

and its a 19 as well

i wonder what the fuck is going on.............

charlie · Post by **charlie** » Fri Sep 04, 2009 10:00 pm

liny poo

http://www.bxproject.co.uk/phpBB3/viewt ... =12&t=2364

citronut · Post by **citronut** » Sat Sep 05, 2009 12:28 pm

what about the flap in the air intake, which opens and shuts the hot air supply from the manifold to carb, (summer/winter)

regards malcolm

french driver · Post by **french driver** » Sat Sep 05, 2009 10:28 pm

Never thought of that flap...good idea.

I did notice this morning the coolant level was down a bit and had to put in 400ml to get it to the correct point. The point being level with the top of the radiator about 5cm below the cap for expansion.

Maybe a airlock problem then? But will look at the other ideas as well when get some time.

citronut · Post by **citronut** » Sat Sep 05, 2009 11:10 pm

the coolant level should be at the bottom of the rad kneck,

regards malcolm

french driver · Post by **french driver** » Sun Sep 06, 2009 3:44 am

It is thanks anyways malcolm.

May have found the problem or at least a cure by winding back an idle screw that is the extra bit for the air conditioning unit. Seems to have sorted the problem.

How I come to the conclussion was everything was fine when I was playing around with it until I decided to flick on the aircon. When I switched off the aircon up came the revs. So the fault seems to be relating to how the aircon interacts with the carb idle.

See how that goes in a couple of days may not be the problem but elimination process.

Post by **mat_fenwick** » Sun Sep 06, 2009 10:38 am

You have air con? A very rare option...at least here in the UK. I've never come across a carb fed A/C BX, just the valvers, Gtis and Turbodiesels. Are you over here or do you live somewhere where A/C is more 'the norm'?
Welcome along by the way!

DLM · Post by **DLM** » Sun Sep 06, 2009 1:18 pm

I think the aircon-specific idle adjustment is an anti-stall measure - the carbs for such a BX are specific to aircon models.

The extra load from the aircon compressor can do a good job of stalling even a diesel turbo at low revs if care is not exercised - I flip the aircon off at junctions as a precautionary measure.

french driver · Post by **french driver** » Mon Sep 07, 2009 8:09 am

well many thanks go to Kiwi for the PM he sent suggesting where to look.

It may be the result of knocking the idle adjustment when I replaced an alternator belt it seems to have occurred about the same time.

You right mat I am not in the UK but I have another of those dreaded antipodean BX models. The problem is now resolved it looks like anyways.