Post by archloafer on Dec 6, 2020 15:29:53 GMT 1
Hi folks
Finally got the 4L1 on the road. Couple of problems evident.
Realise I'm probably going over old ground but thought I'd start the thread as a record of my own troubleshooting efforts, and maybe get some input from people who know what they're doing
The main issue is difficulty starting from cold. It takes about 10 kicks (choke out) before it fires, then it will fire and run on one cylinder for a few seconds and then die. If I touch the throttle it dies straight away.
Repeat a few times and it starts running for longer periods and eventually comes to life to the extent that I can rev it and put the choke in. Seems to be running on the left cylinder OK but the right one is only running poorly / intermittently (judging from the exhaust output). If I rev it gently for about a minute this seems to correct itself and the right cylinder starts running apparently normally, settles down to a nice tickover.
Once the engine has warmed up for 5 minutes or so it starts first kick, seems fine.
2nd (perhaps related) issue is a bad flat spot aproaching 5000rpm. There's not a great deal of power up to this point but it seems to accelerate smoothly and crisply, then a pause when it seems like it won't actually rev past 5. Eventually it does and starts to pick up swiftly from 5 up to about 6 and a half, after which it properly takes off.
... until 9000rpm when it just hits a wall. Issue number 3 - won't go past 9 in any gear. Either the rev counter isn't working properly, or something else is afoot!
Final issue which became apparent when on the motorway is that it's hard to keep it in the power in the higher gears. In 5th or 6th at around 7000rm, if I throttle back a bit down to 6 then try to accelerate it just won't do it without dropping down a couple and nailing it before changing up again. I'm not expecting V-Max grunt from a small capacity tuned 2 stroke, but I think it should be better than it is at the moment.
Suspect that while the above issues might possibly be having some impact on this, it's above the problem area in the rev range so probably just gearing. Drop a couple of teeth on the front sprocket perhaps.
Is there any reasonably reliable method of working out final drive ratios, outside of dyno time, or is it just trial and error?
Some details:
Ported barrels - couldn't give exact details but fairly extensive. Guy I bought it from told me the work was done by Bob Farnham circa 1989. Took the engine to Bob / Steve Wave racing who rebuilt the crank, did a bit of work on the head to lower the compression a touch. They recommended getting some pipes that would allow it to rev out.
So I went and got some allspeeds
Not ideal, but comparing how the bike went when I first rode it (very long time ago but still remember some aspects with crystal clarity) with standard pipes, it was better back then. I recall it used to bog down more at lower revs, seems crisper now. But it would rev to at least 10000rpm, the flat spot deffo wasn't there and the front wheel came up off the throttle in 1st and 2nd, which it doesn't do now. Pretty sure the rear sprocket was bigger though, and it had an oversized Metzeler on the back wheel, which I guess would also factor in.
With regard to the starting issues I'm reasonably confident that the electricals are OK. Stator was originally sent to Westcountry Windings (I didn't know better at the time), who messed it up. Would only produce a very weak spark, bike wouldn't start at all. Took it to Rex's Speedshop who re-wound it properly, tested it. Got a dyna mini-coil and leads, nice fat spark on both plugs. Swapped the HT leads over and still the R/H cylinder is the dodgy one.
Running the standard CDI - possible that's responsible for the bike not revving out? Have a couple of others I can test it out with.
I was using B8ES plugs, but I swapped them out with B9EG (NGK racing rubber resistor caps). That did improve the starting issue marginally, but suspect that might just be because the ones I took out had fouled up after the bike was run several times, but not ridden, before I got it on the road.
I suppose carburation is the most likely suspect. Standard 4L1 carbs. I had the bodies vapour blasted and ultrasonically cleaned before rebuilding them. I did use a Keyster rebuild kit for both, which I gather from reading other posts might not be great quality. Again, didn't know better at the time. However, I re-used the original jets and needles (instinctive suspicion of the Keyster kits, perhaps!?). Didn't write down the jet sizes when I rebuilt the carbs - will check at the next available opportunity.
I did check the float height in each carb using the pipe attached to the float bowl drain method. Set the closed-throttle slide height with the non-business end of a drill bit method, and adjusted the throttle cable using the taking the carbs off and looking into the back of them method - because the lolly stick method isn't possible with a standard airbox.
Been reading about the air correction circuit. I've ordered some 4.5mm brass balls, so will be checking that.
Standard airbox with the snorkel removed and the filter element (temporarily) taken out.
Running premix with Castrol power-1 racing at 33:1.
Anyway, I'll leave it there for the time being, before this post turns into a novel
Cheers - David
Finally got the 4L1 on the road. Couple of problems evident.
Realise I'm probably going over old ground but thought I'd start the thread as a record of my own troubleshooting efforts, and maybe get some input from people who know what they're doing
The main issue is difficulty starting from cold. It takes about 10 kicks (choke out) before it fires, then it will fire and run on one cylinder for a few seconds and then die. If I touch the throttle it dies straight away.
Repeat a few times and it starts running for longer periods and eventually comes to life to the extent that I can rev it and put the choke in. Seems to be running on the left cylinder OK but the right one is only running poorly / intermittently (judging from the exhaust output). If I rev it gently for about a minute this seems to correct itself and the right cylinder starts running apparently normally, settles down to a nice tickover.
Once the engine has warmed up for 5 minutes or so it starts first kick, seems fine.
2nd (perhaps related) issue is a bad flat spot aproaching 5000rpm. There's not a great deal of power up to this point but it seems to accelerate smoothly and crisply, then a pause when it seems like it won't actually rev past 5. Eventually it does and starts to pick up swiftly from 5 up to about 6 and a half, after which it properly takes off.
... until 9000rpm when it just hits a wall. Issue number 3 - won't go past 9 in any gear. Either the rev counter isn't working properly, or something else is afoot!
Final issue which became apparent when on the motorway is that it's hard to keep it in the power in the higher gears. In 5th or 6th at around 7000rm, if I throttle back a bit down to 6 then try to accelerate it just won't do it without dropping down a couple and nailing it before changing up again. I'm not expecting V-Max grunt from a small capacity tuned 2 stroke, but I think it should be better than it is at the moment.
Suspect that while the above issues might possibly be having some impact on this, it's above the problem area in the rev range so probably just gearing. Drop a couple of teeth on the front sprocket perhaps.
Is there any reasonably reliable method of working out final drive ratios, outside of dyno time, or is it just trial and error?
Some details:
Ported barrels - couldn't give exact details but fairly extensive. Guy I bought it from told me the work was done by Bob Farnham circa 1989. Took the engine to Bob / Steve Wave racing who rebuilt the crank, did a bit of work on the head to lower the compression a touch. They recommended getting some pipes that would allow it to rev out.
So I went and got some allspeeds
Not ideal, but comparing how the bike went when I first rode it (very long time ago but still remember some aspects with crystal clarity) with standard pipes, it was better back then. I recall it used to bog down more at lower revs, seems crisper now. But it would rev to at least 10000rpm, the flat spot deffo wasn't there and the front wheel came up off the throttle in 1st and 2nd, which it doesn't do now. Pretty sure the rear sprocket was bigger though, and it had an oversized Metzeler on the back wheel, which I guess would also factor in.With regard to the starting issues I'm reasonably confident that the electricals are OK. Stator was originally sent to Westcountry Windings (I didn't know better at the time), who messed it up. Would only produce a very weak spark, bike wouldn't start at all. Took it to Rex's Speedshop who re-wound it properly, tested it. Got a dyna mini-coil and leads, nice fat spark on both plugs. Swapped the HT leads over and still the R/H cylinder is the dodgy one.
Running the standard CDI - possible that's responsible for the bike not revving out? Have a couple of others I can test it out with.
I was using B8ES plugs, but I swapped them out with B9EG (NGK racing rubber resistor caps). That did improve the starting issue marginally, but suspect that might just be because the ones I took out had fouled up after the bike was run several times, but not ridden, before I got it on the road.
I suppose carburation is the most likely suspect. Standard 4L1 carbs. I had the bodies vapour blasted and ultrasonically cleaned before rebuilding them. I did use a Keyster rebuild kit for both, which I gather from reading other posts might not be great quality. Again, didn't know better at the time. However, I re-used the original jets and needles (instinctive suspicion of the Keyster kits, perhaps!?). Didn't write down the jet sizes when I rebuilt the carbs - will check at the next available opportunity.
I did check the float height in each carb using the pipe attached to the float bowl drain method. Set the closed-throttle slide height with the non-business end of a drill bit method, and adjusted the throttle cable using the taking the carbs off and looking into the back of them method - because the lolly stick method isn't possible with a standard airbox.
Been reading about the air correction circuit. I've ordered some 4.5mm brass balls, so will be checking that.
Standard airbox with the snorkel removed and the filter element (temporarily) taken out.
Running premix with Castrol power-1 racing at 33:1.
Anyway, I'll leave it there for the time being, before this post turns into a novel
Cheers - David
