Wont exceed 4,500 rpm then stalls and wont restart - on route to MOT

[totty]

No, I didn't trust cheap ones to be calibrated correctly or want to pay for expensive ones so I took a chance on a simple device off ebay, I can't link to it now as it's blocked at work but it's essentially some clear tube and some ball bearings. It's workings seemed pretty logical to me and it was quite sensitive so I'm reasonably confident that it will of done the job.

In the upper rev range it kind of splutters and surges and exhaust note goes flat.

I'm considering upgrading to a Boyer Bransden Micro Power Ignition system. On another forum the coils and the mechanical advance have both been named as possible sources and this system would replace both.

[Dave M]

I bought one those ones for my CB550. Worked fine.

[totty]

I've fitted a Boyer ignition kit, but I'm struggling to time it. The instructions say time to the max advance marks at 4,500 rpm. My strobe is normally clear enough to use at idle but it doesn't seem to be able to cope at that high an RPM, and also gives you a shock every time you touch a metal part of the bike once over around 3,000 which makes fine adjustments tricky. I've borrowed a bottle of tipex from work to highlight the markers, if I still can't see them I'll have to take it to someone or buy a new strobe. (although I think I need a new strobe anyway)

A quick test ride shows that it hasn't resolved the problem, it's still bogging at 5,000rpm and being inconsistent above it, although that may be down to the timing.

Cheers

Allan

[notobikeparkingtax]

Have you checked the valve clearances ?

[Yoshi823]

I've fitted a Boyer ignition kit, but I'm struggling to time it. The instructions say time to the max advance marks at 4,500 rpm. My strobe is normally clear enough to use at idle but it doesn't seem to be able to cope at that high an RPM, and also gives you a shock every time you touch a metal part of the bike once over around 3,000 which makes fine adjustments tricky. I've borrowed a bottle of tipex from work to highlight the markers, if I still can't see them I'll have to take it to someone or buy a new strobe. (although I think I need a new strobe anyway)

A quick test ride shows that it hasn't resolved the problem, it's still bogging at 5,000rpm and being inconsistent above it, although that may be down to the timing.

Cheers

Allan

The Boyer-Bransden kit is only timed for idle...the advance & retard is electronic. As far as I remember you line up the leading edge of one of the two magnets with the edge of the centre post of the coil which has the magnetic field induced into it as the magnet passes it. To keep this as accurate as possible I disassembled the 750s advance/retard unit, discarded the bob-weights, ground off the raised bits that locate with the big not that you can use to rotate the crank, then Loctited the retaining bolt into the end of the crank. I was then able to make small adjustments using the elongated slots on the PCB backplate.

[totty]

I set the tappets when I first bought it 350 miles ago, could they cause these symptoms?

The Boyer system I've fitted is "KIT00289 Micropower ignition system for Honda "4" S.O.H.C. Motorcycles". Fitting is as you describe but it does not tell you to grind off the raised bits, timing instructions tell you to line it up the magnets with the posts at TDC then time with a strobe to max timing marks at 4,500rpm. I've ordered a new strobe as mine just wasn't clear enough and kept giving me shocks, but I'm not convinced that setting the timing will fix it.

[matthewmosse]

I seem to recall I had a similar problem before sidelining the sidecar outfit, fraid I can't say I resolved it though. Like you I tried swapping to boyer ignition but no success so problem must lie elsewhere was my conclusion. Tried another set of carbs? That was my next line of attack when I get the time.

[totty]

I don't have another set of carbs to try, I might have to lookout for a set if setting the timing doesn't sort it. I'm reluctant to throw more money at the bike though, I keep saying I'll never buy another vehicle that isn't already in regular use as they're always a pain to get sorted but I keep buying them.

[Yoshi823]

If only you lived closer...

[metalcatfish]

Had these symptoms once, was caused by multiple problems any of which can cause similar symptoms.
Engine kill switch, these are rubbish and dont stand up to the high loads that electronic ignition creates. Electronic ignition fires all 4 plugs simultaneously hence doubling the duty on those silly little switches. Bypass it or replace with something else. Ignition switches, also rubbish but not so bad as the above.
Spark plug caps must be new shiny 5k ohm jobs.
Original coils are good but can overheat when used for EI. Again they get hotter cos they are working twice as hard. Also fail twice as quick. May need an ally heatsink, mine did.
Had no end of problems when switching to EI, All sorted now, Plugs must be changed more regularly.
Also, a binding front brake can cause overheating. Idling too long, they dont like idling. Blocked main jets will cause it to bog down and feel slack, Take them off, take the float bowl off and waste 2 cans of carb or brake cleaner in every orifice you can. Remove jets, inspect, Check float height, this is another common problem, lack of fuel through poorly adjusted floats.

[Yoshi823]

http://www.sohc.co.uk/index.php?topic=2849.0

[totty]

Hi,

The problem existed prior to fitting the electronic ignition.
The coils were replaced as part of the electronic ignition kit, plugs are new NGK irridiums, also tried normal NGK plugs and the caps are new NGK 5k.
Float heights are correct and loads of carb cleaner has been blasted through every orifice twice.
I've used the spray something flammable in the area vacuum leak test 3 or 4 times without any signs of leakage so I think those seals are ok, but if I have to resort to removing the carbs again I'll replace then just to be sure.

I've noticed that it's allot worse when the weather is cold so I'm working on the theory that it's running lean, I'm going to see what effect raising the needles one notch has.
If that fails I'll relay the ignition so I'll keep the ignition and kill switch control but without running the current through them.

[totty]

Has anyone got any idea how you access the needles on these carbs ?
It's a K3 and it's the PD carbs with the sync adjusters under the top covers.
I can't see how you disconnect the linkage and remove the slides so I've just put it back together for now.

[metalcatfish]

I doubt if the needles are your problem but I guess its worth a look anyway. Take off the tank, Take the tops of the carbs off, Undo the philips screw that secures the lifting arm to the rotating shaft.
Get a thin philips screwdriver down inside the slide and disconnect it from its arm. Disconnect the arm being carefull not to lose screws or the little spring and pull the slide out, its easy. If you cant get to the screws gently twist the slide and its arm till it comes off, yourll see what I mean, then pull the whole thing out and then undo the screws inside the slide. Jap screws are made of chocolate so be carefull if there a bit tight. You can do this with the carbs in place.

[totty]

I doubt if the needles are your problem but I guess its worth a look anyway. Take off the tank, Take the tops of the carbs off, Undo the philips screw that secures the lifting arm to the rotating shaft.
Get a thin philips screwdriver down inside the slide and disconnect it from its arm. Disconnect the arm being carefull not to lose screws or the little spring and pull the slide out, its easy. If you cant get to the screws gently twist the slide and its arm till it comes off, yourll see what I mean, then pull the whole thing out and then undo the screws inside the slide. Jap screws are made of chocolate so be carefull if there a bit tight. You can do this with the carbs in place.

Cheers, I'll give it a shot later in the week.
I doubt it as well but I'm getting desparate, I can't see anything wrong with the floats or lower jets and replacing the ignition system didn't really make any difference.
The significant improvement in hotter weather makes me side with it being a fueling issue.