Xflow running on 2 cylinders

[MonkeyBoy]

Hi all,

 

Having problems with my 1700 xflow, it died a couple of years ago (failed hose to oil cooler doing 80 on French motorway and seized up) and so I’ve been slowly rebuilding it, basically a complete rebuild, forged pistons, unleaded valve seats, refaced head and block, new gaskets etc. I had it all rebuilt and running for a couple of days end of last year to get through the MOT then it sat outside over winter, then when I went to use it the hall sensor in the dizzy had failed so I replaced with a new kit, then it was only running on 2 cylinders (1+2) and it seemed that there was no fuel from one of the carbs so I stripped it – it had loads of gunk in and the fuel had a layer of water floating on top so I cleaned it all out including jets etc and put it all together and one of the fuel hoses split so had to replace. Now it still only runs on cylinders 1+2. Cylinders 3+4 are getting a spark, and I double checked the leads were the right way around (and swapped them over to double check).

 

I seem to be getting fuel in the carb – when you look down the carb you can see evidence of fuel. However, if I spray Easy Start into the trumpets it still doesn’t kick in. I checked compression at with throttle open I get 13.5-14.5 bar on all 4 cylinders (this is after running on 2 cylinders for a few minutes so ‘cold’). With the throttle closed I get around 11 bar on cylinders 1+2 but only about 4-6 bar on cylinders 3+4. So I checked the tappets and they were pretty much there (22 thou inlet, 24 thou exhaust) and just needed less than 1/8th turn, but I still get the same compression readings (throttle open and closed) and still only runs on 2 cylinders. I’m a bit stuck and don’t know what to do next – any ideas ??

 

Many thanks

Alistair

 

[Paul Deslandes]

I've no experience of crossflows but I guess at carb and ignition level its just an engine.

 

Lower compressions on 3 and 4 is probably due to them being colder than 1 and 2. You should do this test at full throttle anyway.

 

Can you borrow a timing light to check that 3 and 4 are sparking when they should? Not sure what triggers the dizzy but does it look ok? Presumably it has four lobes of some sort.

 

Have you really cleaned out the carbs? Water can lodge in the airways and fuelways that are bored through the castings so you might want to strip the rear one (3 and 4) and/or blast through the drillings with some aerosol carb cleaner or an airline.

 

If all else fails, swap the carbs over and see if the fault shifts to the other two cylinders. That will eliminate or implicate the carbs.

 

Paul

[jonboylaw]

If the carbs were full of gunk then you might as well strip them down and inspect the jets, could be blocked.

 

 

[andy couchman]

Try replacing the distributor cap? Could perhaps be a hairline crack - or would that only manifest itself at high revs?

 

Also if a carb has been off, it's very easy to leave a wad of paper in the manifold (been there, done that... 😳).

 

Are the carbs connected? Easy to have only one throttle actually working.

 

If the manifold has been off are you getting a water leak into cylinder 3 from a faulty manifold gasket?

 

All I can suggest is doing a thorough go through of everything. Also, take the plugs out and turn the engine over in case 3 and 4 are flooded. Valves all appear to be wotrking OK if you've checked the tappets so you can probably rule that out.

 

Good luck - sounds infuriating...

 

Andy

[MonkeyBoy]

Thanks for all the advice, good stuff, in the end i found out that the carb linkage had worn so sometimes it wouldn't seat properly between the two carbs meaning that one carb wasn't getting enough fuel at idle, so got a replacement from webcon and it now runs on all 4 cylinders Only problem is some carb coughing and spitting but that's a subject of another thread....

 

Many thanks

Alistair