Problem at med/high rpm - Honda Motorcycles - FireBlades.org
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post #1 of 17 Old 09-15-2019, 2:25 PM Thread Starter
 
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Problem at med/high rpm

So the honeymoon period has come to an end

I've got a '93 blade engine in a car and it's been running very well for the last fee weeks that I've had it. I drove home yesterday, all was perfect. Tonight I popped out and after about 5 miles I gave it some throttle and it stopped at 8k rpm, just wouldn't go past it.

I pulled over and it was idling fine, it only happens under load and felt a bit misfire-esque rather than fuel but can't be sure. I drove home and found I couldn't go over about 5k without it bogging down but it idles OK and is OK at low speed.

So, the impossible web diagnosis challenge, what is it?! I'm going to switch out the plugs but I've just popped them out and there's nothing too terrible going on, is it worth a coil switch out do you think? I found these which seem cheap enough:

https://www.ebay.co.uk/itm/Honda-CBR...AAAOSwqVBZX8wC

I'll switch out the fuel filter but it looks clean and the pump is working correctly. I guess the carbs can be prodded and poked too but really after any suggestions I haven't thought of

Thanks

James
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post #2 of 17 Old 09-15-2019, 5:57 PM
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Re: Problem at med/high rpm

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Originally Posted by jseaman View Post
So the honeymoon period has come to an end

I've got a '93 blade engine in a car and it's been running very well for the last fee weeks that I've had it. I drove home yesterday, all was perfect. Tonight I popped out and after about 5 miles I gave it some throttle and it stopped at 8k rpm, just wouldn't go past it.

I pulled over and it was idling fine, it only happens under load and felt a bit misfire-esque rather than fuel but can't be sure. I drove home and found I couldn't go over about 5k without it bogging down but it idles OK and is OK at low speed.

So, the impossible web diagnosis challenge, what is it?! I'm going to switch out the plugs but I've just popped them out and there's nothing too terrible going on, is it worth a coil switch out do you think? I found these which seem cheap enough:

https://www.ebay.co.uk/itm/Honda-CBR...AAAOSwqVBZX8wC

I'll switch out the fuel filter but it looks clean and the pump is working correctly. I guess the carbs can be prodded and poked too but really after any suggestions I haven't thought of

Thanks

James

I see high rpm under load failures as either a blocked main jet circuit in the carbs, or a rod or crank bearing failing. Any noises you could hear? First I would check all 4 for compression and post your results. The coils and spark units on these guys RARELY go bad, but anything's possible.

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post #3 of 17 Old 09-16-2019, 3:22 AM Thread Starter
 
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Re: Problem at med/high rpm

Oh no! Hope it's not that, I didn't hear any scary noises but will do a compression test and report back - thanks
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post #4 of 17 Old 09-16-2019, 8:43 AM
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Re: Problem at med/high rpm

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Oh no! Hope it's not that, I didn't hear any scary noises but will do a compression test and report back - thanks
Another thing to check is your charging system. When they start to fail (stator, reg/rec, battery) it can create similar symptoms as one or all the components start to fail. How much use with the car have you had since you finished it?

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post #5 of 17 Old 09-17-2019, 1:48 PM Thread Starter
 
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Re: Problem at med/high rpm

Compression test done, all done cylinders 150 psi within 3/4 cranks. 171psi appears to be the book figure so not terrible but no obvious drops

Resistance was 3.3 Ohms on one coil and 3.4 on the other

Plugs are on their way so will do some voltage checks when fitted and a fuel pressure test. I did notice a higher than expected terminal voltage, was just over 13V yesterday and after the compression test still up at 12.9V
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post #6 of 17 Old 09-18-2019, 3:01 PM Thread Starter
 
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Re: Problem at med/high rpm

Changed the plugs and fuel filter, no difference. At idle I rev'd it and notice the filter went a little dry but fitted a brand new fuel pump and still can't rev past 8k rpm.

Voltage is solid around 14.8 V when running so nothing too funky

On the noise front, I should add that I was chasing a noise which I had put down to the car panels rattling and hadn't attributed this to the engine but could be. Noticed at high RPM but can't be sure if it is car or engine at this stage

At idle everything is perfect and will rev freely with no knocking or issue at all

The only thing I have left is test fuel pressure but after two pumps I don't think this will yield much

Oh and in terms of use, I've done about 1k miles so far

Is there an easy way to test the main jets or is it a carb strip down? I guess I could quite easily drop the sump and take the big end caps off for a poke around
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post #7 of 17 Old 09-18-2019, 4:48 PM
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Re: Problem at med/high rpm

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Originally Posted by jseaman View Post
Changed the plugs and fuel filter, no difference. At idle I rev'd it and notice the filter went a little dry but fitted a brand new fuel pump and still can't rev past 8k rpm.

Voltage is solid around 14.8 V when running so nothing too funky

On the noise front, I should add that I was chasing a noise which I had put down to the car panels rattling and hadn't attributed this to the engine but could be. Noticed at high RPM but can't be sure if it is car or engine at this stage

At idle everything is perfect and will rev freely with no knocking or issue at all

The only thing I have left is test fuel pressure but after two pumps I don't think this will yield much

Oh and in terms of use, I've done about 1k miles so far

Is there an easy way to test the main jets or is it a carb strip down? I guess I could quite easily drop the sump and take the big end caps off for a poke around
Maybe your cam timing jumped off a tooth. Could be the source of the noise, a bad CCT (cam chain tensioner). Everything else seems on par. Pulling the oil pan won't get you access to much, and may be difficult to get a wrench on the big end bolts. The main oil galley runs almost parallel with the crank.

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It could be some debris clogging the carbs. But don't be forcing too much fuel pressure into them. The bike originally had a pump, but it was a zero pressure "helper", that just moved the fuel along. I took the fuel pump clean off my 93 and run gravity with no issues. The carbs should come off if you're serious about checking them out.

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post #8 of 17 Old 09-19-2019, 2:54 AM Thread Starter
 
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Re: Problem at med/high rpm

Oh blimey that does look busy!

Cam timing jump sounds like it could fit the symptoms and a tensioner was on the hit list anyway - are there any tips or things to consider while having a look?
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post #9 of 17 Old 09-21-2019, 6:36 AM Thread Starter
 
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Re: Problem at med/high rpm

OK so the latest is this:

I took the cam cover off and spun the crank and with the EX line bang on level with the block, the opposing IN line was a couple of teeth out. The chain felt like it had less tension on than I expected too.

I'm not sure how you are supposed to move a tooth so I went for removing the tensioner then I was going to take the cam pulley off, did the first bolt then as I rotated it, it conveniently jumped 2 teeth and so I popped the tensioner back in and called it done!

Took it out for a spin and a noticeable improvement was there. That said, as soon as I got to 8k + it would bog down but it felt different, much more fuelly. It would push through and get to 11k RPM now but spluttering.

I decided the beset thing to do was take it home and refit the original fuel pump in case the new one was the issue, this made it much worse! It would really bog at 8k and not push through again

So I was 2 teeth out, my fuel pump was apparently failing and I've still got something to find.

I guess I'll try and identify the original pump that was on there and fit a new one in case that is a factor and I'm also going to check that timing again.
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post #10 of 17 Old 09-21-2019, 7:34 AM
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Re: Problem at med/high rpm

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Originally Posted by jseaman View Post
OK so the latest is this:

I took the cam cover off and spun the crank and with the EX line bang on level with the block, the opposing IN line was a couple of teeth out. The chain felt like it had less tension on than I expected too.

I'm not sure how you are supposed to move a tooth so I went for removing the tensioner then I was going to take the cam pulley off, did the first bolt then as I rotated it, it conveniently jumped 2 teeth and so I popped the tensioner back in and called it done!

Took it out for a spin and a noticeable improvement was there. That said, as soon as I got to 8k + it would bog down but it felt different, much more fuelly. It would push through and get to 11k RPM now but spluttering.

I decided the beset thing to do was take it home and refit the original fuel pump in case the new one was the issue, this made it much worse! It would really bog at 8k and not push through again

So I was 2 teeth out, my fuel pump was apparently failing and I've still got something to find.

I guess I'll try and identify the original pump that was on there and fit a new one in case that is a factor and I'm also going to check that timing again.

So no new tensioner or chain? I would expect it to jump again if that’s the case.

Is your tank not mounted above the carbs? I think you might have too much fuel getting in there. Can you gravity feed and see if it’s any different?

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post #11 of 17 Old 09-21-2019, 9:03 AM Thread Starter
 
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Re: Problem at med/high rpm

I've ordered a tensioner but simply adjusted it and it seems good now

How are you supposed to move a tooth by the way, was I right to take the cam pulley off?

The tank's mounted at the back of the car, might be tricky to gravity feed it unless I jack it up and try it on the drive but I'm not sure if 8krpm with the wheels off the floor will do it, might give it a try!
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post #12 of 17 Old 09-21-2019, 1:03 PM
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Re: Problem at med/high rpm

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Originally Posted by jseaman View Post
I've ordered a tensioner but simply adjusted it and it seems good now

How are you supposed to move a tooth by the way, was I right to take the cam pulley off?

The tank's mounted at the back of the car, might be tricky to gravity feed it unless I jack it up and try it on the drive but I'm not sure if 8krpm with the wheels off the floor will do it, might give it a try!
Ok, I may have missed that you had an adjustable tensioner.

Are your cam sprockets slotted???

I’m trying to visualize what you did. You removed 1 sprocket bolt rotated the crank and the sprocket moved 2 teeth on the chain?

With valve spring pressure the cam will be hard to keep in one place and would probably jump around. Being the internet, please excuse any ignorance in my part, I try to remember everyone I help, but do you understand the timing on these old girls? (#1 TDC, cam lobes pointing away from each other and the IN and EX lines lining up with the top of the head)? Just making sure. I know you’ve posted pics in the past, if you could post another if your cams and chain etc it would speed up my dense brain Hopefully it’s still just a small adjustment with the timing. Back in the day I thought I had my cams degreed properly, only to find out that the intake was so far retarded that I’m surprised it ran as well as it did at all lol

Carry on sir

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post #13 of 17 Old 09-21-2019, 1:18 PM Thread Starter
 
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Re: Problem at med/high rpm

Ah apologies, I didn't realise there were differences - I took a 10mm bolt out the tensioner and used a flatblade screwdriver to tension the chain.

Cam sprockets aren't slotted, I was going to remove a pulley, rotate it and refit it, wasn't sure if that was the usual approach?

I thought earlier it might be easier with a pic and I'm happy to say I took one!

Yes you're correct, one bolt out the inlet side pulley then as I spun the engine (not related to the bolt I don't think, just the tensioner removal), it skipped to what I think is the right place

Yes thanks for checking I'm no fireblade expert at all but I did as you described

Thanks as always for your input
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post #14 of 17 Old 09-21-2019, 1:28 PM
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Re: Problem at med/high rpm

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Originally Posted by jseaman View Post
Ah apologies, I didn't realise there were differences - I took a 10mm bolt out the tensioner and used a flatblade screwdriver to tension the chain.

Cam sprockets aren't slotted, I was going to remove a pulley, rotate it and refit it, wasn't sure if that was the usual approach?

I thought earlier it might be easier with a pic and I'm happy to say I took one!

Yes you're correct, one bolt out the inlet side pulley then as I spun the engine (not related to the bolt I don't think, just the tensioner removal), it skipped to what I think is the right place

Yes thanks for checking I'm no fireblade expert at all but I did as you described

Thanks as always for your input
Thanks! I get it now. The tensioner IS NOT adjustable, it just works on spring pressure. When you take that 10mm bolt off the back there is a slot for a special tool that unwinds the tension for valve adjustments. It then fits in the slot to hold the tension off the chain guide. I believe you damage it if you “screw it in”. I would just get a new one. I’ll post a pic.

Also, forgot to add about the position of the crank for TDC, but I’m sure you got that spot on as well. Your pic looks dead nuts on


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Re: Problem at med/high rpm

Oh mine is definitely broken then!! It was simply winding in when the screwdriver was turned anticlockwise and wound out the other way, no spring pressure at all!

I've got a solid one with a lock nut on it's way.

At least I got the match marks right

I've got a couple of coils on order for the sake of it and I'll have a play with measuring fuel flow to ensure I don't exceed a couple of psi too. Hopefully I'm on the right track, will ping an update when I can
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