hot/cold exhausts

[ChrisC]

Hey Fellas, got an old C B 400t dream...yea yea heard it all before....playing around with it trying to make into something it isn't ! got it running this morning after new parts in carburetters(have not been balanced yet) and the two exhausts no longer have a balance/ collecting box between them .Question is one exhaust is running cold ,and one is much warmer,though the engine is responsive and ticks over fine. Buggered if i can remember what causes it and can't find anything in the haynes.But is a difference in exhaust temperature just the carbs need balancing.
cheers chris

[tony.mon]

First balance carbs; because you have separate pipes you can do this well enough by feeling exhaust pops on your hand at the silencer ends.
Balance until pops feel the same.

Swap hands to make sure.

If there's still a temp difference in downpipes, swap over plugs, then try again.
if there's still a difference, swap coil/ht leads, etc, etc, one thing at a time.

If the cold pipe swaps to the other side, whatever you've just swapped is the culprit.

But something's not right.

[benny hedges]

just a thought.... you haven't got one prosthetic hand have you?

[ChrisC]

Thanks for the info Tony...I'll try it tomorrow....and Benny no i haven't got a prosthetic hand....anymore the bast**d stuck to the hotter exhaust pipe

[ChrisC]

Hey Tony, Tried changing coils over, have got new plugs in and have good spark on both cylinders,but cold exhaust side plug is too wet, I don't think it is electrical. checked float level again in carb.... seems correct .checked air screw 3turns out the same as the other cyclinder,hope thats right Haynes manual is vague on this. ......any ideas would be very grateful.....chris

[AMCQ46]

have you checked the compression is the same on each cyl, and that the carbs are set up exactly the same. not just balance, but are the jets / diaphrams all good and clear....are the choke mechanisims working etc

if it has been standing a long time the jets can get some very solid contamination in them that wont be dislodged by an airline, or carb cleaner. I would advise against sticking a wire in to clean them out, as the brass is soft and steel wire will scratch the bore and make it bigger. my solution is to soak in carb cleaner, then set light to it! the thermalshock will then allow the blockage to be blasted out with an airline. as a last solution you can use a copper wire from small strand electrical wire, as the copper is much softer than steel.

Also if standing a long time any rubber parts will perish, so they have to be on the list to investigate, seals and diaphrams for choke and slides and carb rubbers, float needle face....

once you have the compression and sparks sorted, then I would swap bits of the carb [jets, diaphram, choke, float assy] and see if it moves

[ChrisC]

1st up...Thanks for the interest and help fellas, the bike has been laid up for some considerable time but was running ok, i drained the petrol out of the carbs and dumped the old tank(rusted) and laid the bike up. Now got new clean tank but when i fitted it on petrol leaked from the carb, so bought new carb kit,float jets,needles,rubber o rings but there was no vacuum diaphrams,so haven't disturbed them( Next job). ran the engine today choke working fine and both sliders appear to drop equally but noticed idle speed has now gone higher even after backing off the main screw which controls both carbs, one cyclinder still running hot, other still cold...with wet plug. I'll try and get my hands on a compression tester in a day or two as i'm helping a mate out the next couple of days . cheers chrisc

[benny hedges]

wondering if some rust has found its way in....
might be worth taking the carbs apart again & check the pilot jets, particularly the holes in the sides

[ChrisC]

Thanks for that Benny thats well worth a check too

[blob748]

Hi, compression test, just remember to open the throttle fully when you crank the engine over, and to still earth the spark plugs.

[ChrisC]

cheers for that blob 748,it goes on the list of things to remember only just got home 15mins ago so no messing with the old bike today,or until next Monday now...

chrisc