1&2 not firing.

[Andy1976]

Hi Guys,
I've had to take out my engine to cure an oil leak (More on this later ). Before I removed it I started it up to double check where the leak was coming from. It took ages to get it started and when it did finally cough into life it sounded really rough and sloppy and the throttle response was sluggish.
Anyhow, It's running and I'm on all fours trying to see where this oil is exiting from, when I accidentally banged my forhead on the No.1 header pipe!!
This is when I found out it wasn't running right, as the pipe was stone cold. On further inspection, No.2 was cold too, 3&4 were hot.
I pulled the plugs and they were all black and sooty, (running rich/weak spark i think) but 1&2 were caked in oil, the threads and the tip were covered in it.
Could this be why it's not firing properly or do you think it's something else, IE HT leads pooped, or a bad connection somewhere?
I'm stripping the carbs down again tommorrow to see if owt's blocked up.
Also, it was making a poppin' noise similar to a backfire as if one of the pots was trying to come to life (RPM's increased with every "pop").
What should I be checking to fix this?

Cheers
Andy

[Spitfire]

Hi Andy, no doubt an expert will be along soon but I'll fill in until they arrive, I take a very simple view on this, 1&4 or 2&3 problems look at the electrics, points, coils, leads, plugs, plug caps, timing.
Any other combination, look at air filter, carbs, exhaust, compression.
A good start is to make sure that the basics are right (points, timing, tappets etc) before becoming fixated on one issue.
Having said that what exhaust have you got fitted, mine has the standard down pipes and a BSM Muffler, as the down pipes are different lengths so the mixture varies from cylinder to cylinder, from too rich to just nice.
The BSM muffler was too restrictive and I was running on 4 then 3 then 2 cylinders due to plug fouling it was driving me nuts until I drilled 4 small holes in the muffler. Now no more fouled plugs.

Hope this helps

Cheers

Den

[SteveD CB500K0]

I don't know if true for your model, but on some of the fours there are two feeds from the fuel tap to the carbs. 1&2 or 3&4 not running was always a symptom of fuel starvation in one of them.

[Spitfire]

Steve is right about that, the single pipe from the tap splits in 2, one to 1&2 and the other to 3&4, note also on the F1 that there are sneaky little filters that can only be accessed by removing the float valve set, mine were full of rust.

Cheers

Den

[Andy1976]

It seems to be a fuel problem. Also i've drained my fuel tank to fit a new fuel tap,and I can hear what seems to be grit in the tank. What's the best way of getting rid of it? I had a look inside it and can't see any evidence of rusting.
There didn't seem to be anything that resembled a filter either, so should I fit an inline one?

Thanks
Andy

PS  Den, the exhaust system is a Motad 4-1

[Spitfire]

Hi Andy there should be some mesh on the inlet to the petrol tap, plus there are individual filters on each carb.
To check the individual filters remove the carb float bowls, then making sure that you do not mix them up remove the four floats and needle valves (or do it one at a time), then using a 10mm spanner (or socket) remove the needle valve housing, the rust etc will be on the filter and in the carb.
Don't ask me how I know but be very careful doing this as you do not want to break the little legs that the floats hinges off if you use a spanner !
Here's the filter

and this is what was in it


Cheers

Den

[Andy1976]

Hi guy's
Thanks for your replies.  I've done some checks this aft, got a spark, got fuel getting in (plugs wet), but no bang (only on 4 now).

I'm going to do a compression test tomorrow, what should the readings be?

I've a funny feeling it maybe a head gasket problem.

Cheers
Andy

[Andy1976]

Test results  No.1  135 psi
                  No.2  120
                  No.3  110
                  No.4  150

This was done on a cold engine as it won't run properly (only on No.4) to get it warm.

Could this be the head gasket blown?

Cheers
Andy

[Spitfire]

Don't think this would be a head gasket, it's an air cooled motor so the pressure would find it's way out somewhere (breather or external head/barrels) and would be fairly obvious, more likely rings/bores, but the test may not be that accurate if the engine was cold.
You could still be having carb/timing issues, have you checked the valve clearances, they could be causing a lot of your problems including compression.

Cheers

Den

[Andy1976]

Hya Den,
I'll double check valve clearances tonight, I also found out that I should've had the throttle wide open when I did the comp test so I'll re do that as well.

Andy

[mick]

Hi Andy how you getting on with 750?

[Andy1976]

To be honest mate I've not really been near it. It's starting to get me down a bit. I may have an hour or two on it tomorrow once I've got the grass cut. The bike really needs a full strip down and everything cleaned up. It will give me something to do over the winter months I suppose.

Andy

[Yoshi823]

I use a leak down tester to check where the problems are.This 'Sun' item compresses the relevant cylinder to be tested via the spark plug hole with the valves both closed.Then I listen out for escaping air in the airbox (inlet valves),the exhaust pipe end (exhaust valves) or the oil filler cap (on a 550) or a tappet cover on the 750 for there to be heard air escaping meaning a piston ring problem.The leakage is measured using a dial to see how the other cylinders compare.

But in this threads case it sounds more like carbs, as the fine sediment can get past the filters and is more likely to do with leaving the bike on it's sidestand is the reason why it started with cylinders 1 and 2,thwn number 3.
Check the primary jets as well as the air screw drillings.Clean using carb cleaner spray,easily available from Halfords.

As far as the dust in the tank is concerned,I made up an adapter from the house vacuum cleaner and connected it to the tank...and gave it a good shake about.Job done.