Project The Second Fizzer

Well I'm fast running out of ideas. The reg/rec shat itself so swapped it out and getting good readings now, recharged the battery up again. Not sure what happened there but fixed. To recap:

1. Stator readings good, around 20 amps AC
2. Charging good, reg rec swapped out as above. Readings about 13.5V at idle.
3. Fuel pump is a question mark (see below)
4. Needles set back to stock (middle notch)
5. Pilots set back to stock (3 turns out)
6. Tank of fresh fuel, flowing fine through fuel tap
7. Compression seems fine, bike starts almost immediately with no need for choke
8. Checked position of main jets, seem to be correct as they are different between 1 & 4 and 2 & 3. Seem clear etc.
9. Fuel levels seem OK, float needles aren't jammed all seems good (noting this carburetor ran the other bike with no issues)
10. No tears etc in diaphragms, slide movement all good
11. Engine is freshly timed with clearances done and new rings
12. New plugs. Swapped out coils for other running ones with no improvement.
13. Battery is OK, holding charge fine
14. Air box/air leaks/connections etc all seem fine
15. EXUP seems to be operating fine, I did change the motor just in case to another working one as I was afraid it could have been intermittent.
16. Tried a side stand bypass with no improvement
17. New fuel filter

Damn if only I knew what the heck was going wrong I could just fix it... been over the bike so many times... really open to any other ideas as the moment. I'm starting to think revisiting the clearances and maybe even checking the rings by pulling the cylinder head is a good idea. It doesn't make logical sense to me but that area is the only place I haven't really checked.

The bike seems to run a bit boggy down low but I expected that since I reset everything to stock (had to lean up the needles to get smooth running on the previous engine). It chugs a bit but is mostly OK up to 12K rpm but won't go over that. Very hollow sound that seems to be slowing the engine down but I am not sure it's boggy in the same way as flooding would be.

I've tried pulling the choke to test the lean problem theory but it makes no difference... I'm now moving away from fuel issues. I did put the needles at the richest setting and the bike would hardly run and was massively boggy - just to test it.

The new fuel filter seems to run with a low fuel level, not sure if that's an issue or not. Previously I could run the bike without the tank attached until the carburetors ran out of fuel (I had even run out of fuel myself while riding) so the fuel supply shouldn't logically be the cause of this issue.

All the help has been much appreciated so far, I've tried to approach everything step by step (one thing at a time) and with some logic to track what I have been changing. I am comfortable that everything stated above is accurate and the bike should logically run fine... but any ideas are welcome.

What about main jets in these bikes, can someone confirm what I have read perhaps?

Top one is main jets. Not sure what the clip means though, I'm rusty on that. What is the 3/5 and 3.5/5 again?

 

Thanks. Forgot to mention I swapped out the CDI with no improvement either...

 

Good point, might do that as well, not a big effort considering what I've already been through. The reason I was moving to top end is because I thought it might be the exhaust valves being held open too long at higher RPM so my last guess is that the timing might be out a tooth or so. Something like that may only profess itself under high load...

Rings went through the same process I always use, which is basically put them in, clock them and start her up. Never had an issue doing that before although some may disagree with my lack of attention to the finer detail (ring end gaps etc). I just figure if it goes, starts up without choke etc once the rings bite then she's good enough for me. That was the case again so process seems still OK.

Will let you know. Any other ideas welcome.

 

@my67xr so I imagine that means the "spacer" on two of the cylinders (2 & 3) must be slightly thicker than the other two... interesting I haven't ever bothered measuring that thickness but I do vaguely recall someone mentioning it in another thread.

@Andych I'll test the theory for sure. I am guessing the compression numbers will be fine but the more I think about it the more I am expecting to find myself a tooth out on the exhaust cam. That would explain why I get good compression, but the inefficiency of exhaust gas extraction from the chambers (probably due to the lobe opening the valve later than required) is giving that hollow sound with a loss of power. Just a theory, but will investigate along with a compression test!

 

Something else I will double check for sure, good call.

 

Ah I don't have that shim. Missing from all 3 of my carbies... hmm... And yes you beat me to it because I just reminded myself that the main jets in the 3LN3 carbies are 1&4 97.5 and 2&3 100 - I was a bit confused for a second lol.

Just checked them all - all good so that eliminates that as a potential issue. Moving onto compression/timing now.

 

Ok so the timing... looks borderline to me. I took a couple of different angles so you guys can better see what I am seeing. The intake is probably OK but I'm not sure about the exhaust. I think if I move it by a tooth it will make it worse in the other direction but I'll try that anyway to see where it gets to. Cam chain is probably stretched hence it's not exactly "bang on". I do have a spare new cam chain but I was saving it for later... hmm....

EXHAUST:



INTAKE:

 

@ruckusman you might have just saved me, mate thanks. I had to read that twice until I wrapped my head around it because it got me confused for a second there...

I think that proves there is a mistake on my part - I was trusting the keyster kits when in fact they are wrong, they are the opposite to what they should be it seems. The guy from MSW marked them for me, he either marked them backwards or they are simply wrong in the jet sizing. I had to go back to the parts diagram to double check but that is spot on. The notation on the right is particularly important for the main jet, made me revisit when you mentioned it .

The other confusing things is BOTH my other 3LN3 carbies had the jets the wrong way around... careless of me to make assumptions though. Will reassemble now and see if this has fixed the issue.