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Request for advice - Rapide 276 Carburettors

BlackLightning998

Well Known and Active Website User
VOC Member
Afternoon all,

I'd be grateful for any advice Forum Members can offer with a strange carb problem that I have just picked up.

The bike is a C Rapide, 12 volt Pazon Ignition and recently snapped a front carb throttle cable at the throttle end.

The bike was running fine before, it has air filters push fit onto the carb bodies.

The bike has unusual 276's on it, bolt on flange from a bike other than a Vincent but they have been nicely done and nicely set up - I have done 2800 miles on it with just John Coates doing a carb tune for me and it running like a different bike after that.

When the cable snapped I ran it home about 10 miles at 30/40 miles per hour with the front cylinder running on tickover once the cable snapped.

So, what I've done:

1 - Tank off
2 - Carb top off, slide and needle out to disconnect old cable
3 - Make up new cable and fit, replace slide/needle unit
4 - Carb top back on as before
5 - Replaced rear carb throttle cable at same time
6 - Refitted tank
7 - Sync'd the throttle opening on the cable adjusters
8 - Changed the oiled front plug - running NGK 7's
9 - Went for a run and found the jet body nut loose and petrol around the base of the carb body (I hadn't touched it that I know of - maybe nudged the float chamber and that has done the deed?)- tightened.
10 - Went out today - 10 miles into a run the front plug fouled and bike went onto one cylinder - running very rich when I took plug out.
11 - Hadn't touched the settings on the slide or air on the carb that I know of.
12 -Tried opening the air screw - didn't seem to make much difference as it was the one and a half out at least. Started the bike - ran on one cylinder again.
13 - Whilst riding along, took off the air filter on the way home - seemed to make a huge difference (weakened mixture I guess by allowing more air to flow and bike ran smoother as a twin all the way home.
14 - Whilst riding and pulling plug lead off the rear cylinder, when I open the throttle the bike bogs down, I can look down and see petrol spitting out the front carb bellmouth.
15 - When I do it the other way around, the rear carb pulls cleanly.
16 - Plug still black and sooty when I got home (30 miles).

What is puzzling me is that everything was working fine before and now I have it running very rich to the point it fouls the plug and goes onto one cylinder.

The only other work I have been doing is replace the dynamo which unfortunately fried itself because I had not checked what bulb was in the headlight when I bought the bike and it transpires that it has a big 55/60watt halogen thing - mmmm - one nicely cooked dynamo which threw commutator segments.

On the carbs and rich running - has anyone come across something similar before and can point me in the direction of anything to look at?

Much appreciated all.

Regards

Stuart
 
Last edited:

john998

Well Known and Active Website User
VOC Member
Carb problems

Hello,
Only two thought come to mind, Have you got the slide needle back in the correct groove, if so I would remove the carb and make sure that the main jet is in place.
I have ridden my twin with a cable broken, but feel it is hard on the motor.
Regards John.
 

BlackLightning998

Well Known and Active Website User
VOC Member
Hi John

Hi John,

I didn't disturb the needle, which is in the second slot (which I think is the "standard" setting to the extent there is one) - interestingly the needle in the rear carb is one slot lower.

I suspect that taking the carb off and having a good look, clean, blow and wipe is the best solution - the bike was running fine before and now not - so surely only the things I have touched could have caused this fault?

I wouldn't have thought I have done any lasting damage running slowly for 10 miles on one cylinder do you?

I know now that removing the plug is the preferred option when doing this next time though.

Thanks for taking time to reply - perplexing....

Stuart
 

Len Matthews

Well Known and Active Website User
VOC Member
It is possible to drop the slide in back to front,i.e with the cutaway facing fowards. I know, I did once and wondered why the poor old thing was running so rich. Peering up the bellmouth soon revealed the reason!:)
 

BlackLightning998

Well Known and Active Website User
VOC Member
I ran in the garage to check that - no, it's right

Hi Len,

Many thanks. I ran in the garage to check and no, the cutaway is facing rearwards to the bellmouth of the carb. The hunt continues.

Cheers

Stuart

It is possible to drop the slide in back to front,i.e with the cutaway facing fowards. I know, I did once and wondered why the poor old thing was running so rich. Peering up the bellmouth soon revealed the reason!:)
 

BlackLightning998

Well Known and Active Website User
VOC Member
What a great excuse to stop polishing.....

Hi Ossie,

I'll have a check this evening and see all is OK - I think it should be fine as the bike has push on air filters which have been there since I bought the bike.

Thanks for your thoughts.

Stuart

make sure the holes at the bellmouth intake are clear had mine full of solvol polish too much cleaning over the years.
 

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