Author Topic: Hesitation after @ 4500 rpm  (Read 908 times)

Offline MrDavo

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Re: Hesitation after @ 4500 rpm
« Reply #15 on: April 26, 2022, 11:33:12 PM »
It was me who had fuel starvation on my Z1-A due to a dodgy pattern fuel tap, but this isn’t similar, your bike ran ok and then it didn’t.

I did have issues with my CB750 K1 running rough, though, after I’d rebuilt the engine,  which turned out to be rock hard ancient HT leads into which the plug caps had been screwed so many times that there were only a few threads of copper left. It all looked ok and the caps screwed on tight, but I had intermittent plug fouling and cylinders cutting out and coming back for no apparent reason. CB750 leads come permanently attached to the coils, you can’t change them without clever surgery, there is a thread on how to do this somewhere. I wanted the bike sorted properly, and was dubious about 50 year old coils anyway, so I made a large contribution to the David Silver retirement fund, and put new genuine coils, with leads, on. The bike ran perfect after that.

This may not be your problem, but worth checking out.

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Offline Oggers

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Re: Hesitation after @ 4500 rpm
« Reply #16 on: April 27, 2022, 10:02:56 AM »
Lobo

Difficult to assess which cylinders are misbehaving. It seems to run OK-ish below 4500 or so, then just runs out of power after that. I can wind the throttle fully open on the road, and then nothing - it remains at @4500 and no more. At a standstill it will rev all the way - which is why I was thinking fuel related. I will try replacing the condensors as one seems to be misbehaving. Ignition on, open points, then sparks across one set of points - which there should not be. Other condensor looks fine.....

Davo

HT leads are pretty new and decent ones. I will check all HT connections though. Simple push fit...Coils could be an issue for sure, but keep that for later....


Offline Laverda Dave

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Re: Hesitation after @ 4500 rpm
« Reply #17 on: April 27, 2022, 01:28:10 PM »
It may sound stupid but......Are you sure there is nothing blocking the air intake below the seat ( I am assuming the Z650 has the air intake under the seat as most SOHC do and as my Z400J has as well). Theres nothing attached to the underside of the seat pan such as a document wallet that may be flapping open when the seat is closed and blocking the air intake? Likewise, is there anything that may be blocking the air inlet between the air filter and the air box to the carbs? It could well be the condensors though, just a bit odd that it happened directly after filling up but then again this is what happened to my indicator relay last week.
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Offline Oggers

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Re: Hesitation after @ 4500 rpm
« Reply #18 on: April 27, 2022, 02:03:30 PM »
Dave

Pretty sure nothing blocking the air intakes - which is indeed under the seat, but I'll check it out. I've known stranger things to happen! Condensors - hopefully that will be the issue. Perhaps after turning the ignition off/on at the petrol station, one condensor just gave up...who knows. If it is not condensors, then I'm stumped  :'(

Offline Lobo

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Re: Hesitation after @ 4500 rpm
« Reply #19 on: April 28, 2022, 12:09:40 AM »
Oggers - my previous post was suggesting a method to determine which cylinders are misbehaving. By chopping the engine at problem RPM, rolling to a stop and then pulling the plugs, you may find one / some are wet / cooler than others, which would indicate the problem cylinder(s). Armed with that info will help you massively in determining the cause.

Offline Oggers

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Re: Hesitation after @ 4500 rpm
« Reply #20 on: April 28, 2022, 02:01:26 PM »
Lobo

If new condensors don't sort it, I'll give it a try....

Cheers


Offline philward

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Re: Hesitation after @ 4500 rpm
« Reply #21 on: April 28, 2022, 05:20:13 PM »
I have had condensors go on me on 2 separate occasions and in both cases, the symtoms where the same. The engine misfired as I accelerated - surging then holding back as I rolled the throttle on, This was across the whole rev range and not just at higher revs.

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Offline Lobo

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Re: Hesitation after @ 4500 rpm
« Reply #22 on: April 28, 2022, 10:24:21 PM »
Oggers, have reread your initial post, and see you have an additional in-line filter.

If no joy with other routes, consider taking this out for a short trial. I too used one in a small Yamaha, which would loose power at WOT (on hotter days), but run fine at small throttle settings. The in-line filter was hard to see as buried in the crankcase along side the carb, but upon inspection it appeared only half full, and somewhat airated. Removing it solved the issue.

I’m guessing it was fuel vaporisation - a fairly well documented phenomenon. Typically it rears it’s head when an engine has been switched off for a while, allowing heat to soak into the fuel lines. This fits with your petrol station fill up…

Worth a try I’d guess if al, else fails.

Offline Oddjob

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Re: Hesitation after @ 4500 rpm
« Reply #23 on: April 28, 2022, 11:49:12 PM »
Have you got one of those bottles that hold fuel while you sync carbs? Just thinking, try fitting that if you have and go for a quick run to see if it's a fault inside the petrol tap.
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Offline Oggers

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Re: Hesitation after @ 4500 rpm
« Reply #24 on: April 30, 2022, 12:17:11 PM »
Chaps

I am very pleased to report I have just ridden the bike very quickly up my very convenient, quiet test hill just outside the village, and I can report all seems well. In fact far better than before! It pulls like a train. The problem did indeed appear to be condensors, and in all probability, one of them was on the way out creating less than adequate sparking before it finally gave up.

Couple of points - pun intended....

Intially I must have inserted the fork connectors of the condensors to the small bolts incorrectly. I do realize there are insulating washers and that the contact fork terminal sits in there also. Initially the bike would not start after replacing the condensors. I then fiddled about further, and inserted both fork terminals under the washer which sits under the head of the bolt. The insulating washer follows this, which would seem to insulate the bolts/forks from a bracket and thus the contact breaker plate? When it would not start, I feel the fork connector(s) may have been in contact with bracket/contact breaker plate. I am no sparkie so lesson learned perhaps....which is carefully note how things are connected/attached before removing them!

Everything pointed to fuel as the problem. I guess the condensor died when I turned the ignition back on at the petrol station. One for the brain's hard drive -  not to be wiped. Thinking about it, the bike now performs so well that it may be worth replacing condensors on other bikes as a matter of course. I have no idea how these things behave and if condensors degrade over the years, but for £10 from Fleabay, it may be a worthwhile thing to do on the 400/4 and the GS1000.

Very many thanks for all your suggestions and help. I find these forums are a truly beacon of kindness in this increasingly disagreeable world. 


       

Online Sesman

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Re: Hesitation after @ 4500 rpm
« Reply #25 on: April 30, 2022, 01:02:29 PM »
Let’s all bid on it then FHO at the end?

 

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