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quick question for any experts.. I know if cam timing is out, it can make a bike not rev out (which is my problem) - won't rev out. (perfect up to 9k)

But - (cam timing) would it sound perfect and rev out perfect in the paddock as normal???
It only wont rev out when its under load - it is not a (fuel) pump issue, the only thing I have not checked as we were rushing around is plug colour/ secondary throttle valves and injectors - but it's tricky as it maybe vibration related, it might be temp related but we never give it maximum before it's all warmed up.

If I pull into the pitlane - static - when it's been doing it - it will rev out in neutral again perfect???

This motor has had a full rebuild, the guy who built is an expert and raced gsxrk5 when it was new - I really can't see him getting it wrong but I want to check it - I know it wont be stock timing but I do have another motor to compare it to - assume he uses similar timing.

I am slowly going through things and running out of ideas - back in the workshop next week. Need to get it on a dyno because my a/f reading seem ok when driving.

which tells me it's fueling and igniting correctly which only leaves valve timing. Although I might have a voltage issue at high revs - need to check it but its charging ok at tick over....
Had this issue last year on a different motor and it went away after some fiddling so its a weird head scratcher.

any advise appreciated :)

Premium Member
2,086 Posts
Well, here are some thoughts of mine - for whatever they are worth:

Cam Timing

1. If it jumped a tooth on a cam, it could do weird things. But it could only jump a tooth in one direction and still keep working

Going the WRONG direction (retarded on exhaust, advanced on timing) and the motor would most likely shit all the valves when the pistons hit them. completely break down or blow up

But, WHY would a cam be off a tooth? Did this occur right after doing cam work?? Having the cams / tensioner off or disassembled, then assembled incorrectly? Thats about the only way I'd see it getting a tooth off on cam timing

2. If you are talking about cam timing in terms of adjustable cams, and degreeing them back and forth, if you were off a little bit, say your target was 105/105 (for sake of argument), and you were actually at 100/100 or 110/110, That would make a quite noticeable difference in power delivery, but it wouldn't just hit a certain RPM and flatten out. One direction could make the pistons and valves hit each too possibly

Of course, if you had adjustable cams, and the bolts that hold the cams to the adjstable sprockets came loose (improperly tightened, not locktited, etc), it could make the cam timing on one cam get way out, might seem like a cam was off one tooth....

Other stuff - are you sure, and I mean SURE, absolutely 100% positive its not a fuel problem??? What did you check and try to confirm that?

A restricted fuel system (weak pump, dirty fuel filter, CRIMPED FUEL LINE, etc) can cause the engine to hit a certain RPM and go flat while under load. The engine is getting X amount of fuel, and it can only make Y amount of power with that, meaning it can only get to Z rpm. But when the engine is under no load, it takes little fuel, so it can rev easily

I got some dirty race gas once, without knowing it of course, and it caused me a bunch of problems. Bike would get to a certain RPM and then just nose over, it just wouldn't rev past that

Turned out the fuel I had gotten had a bunch of crap in it, and it clogged the fuel intake filter (the little screen on the pump). Small filter, doesn't take much to clog it up!

This is all on my K8 1000 (now a 1070)

Anyways, I ended up cleaning out the filter and pump so I could run it again at the trackday which was coming up soon, but i ended up getting a new (used, but like new) pump assembly to replace it, just so i didn't have to think about it again

One other thing - I've done a fair amount of work on the 1K4 and 1K8 I owned (still have the K8), but haven't done much work at all on the K5/6. Just didn't have one or a friend with one who needed much work. So this may or may not apply

Anyways, on the K4, the factory fuel line between pump and throttlebodies could get kinked fairly easily. Soft rubber coating on outside, but harder plastic on the inside, so if it got turned at a sharp angle it could pinch off the fuel supply. I never had a PROBLEM with the K4, never saw any bad effects from it, but I ended up getting a replacement fuel line anyways (which turned out to be a slightly different shape too, seems like the OEM made an update / change along the way)

So, I've always kept an eye on that. it looks like its something that could happen fairly easily on a bunch of GSXR's in the wrong circumstances. Mainly just wiring and other things around the backsides of the throttlebodies and the area where the fuel line goes - if it were to hang up on something there it could get folded / pinched when the tank goes down

*shrugs* i dont recall this ever being a notable problem, but just something i've noticed, that COULD happen..... so I always keep it in mind

Oh - one last thing - if you shut the bike off immediately after it has that problem and open the gas tank is there a big WHOOSH or sucking noise? If so, you could have a tank venting issue. Somehow the vents that are supposed to allow air in (such as the gas cap, but other places too) so that fuel can go out, if they get really clogged up its really hard for the fuel pump to get fuel out, so it can starve the engine of fuel

Other than that, there are a bunch of different possibilities - problems with aftermarket electronics (if you have any), a cam position sensor not reading correctly (maybe happen with an aftermarket cam with the cam position sensor pin pushed in too deeply, maybe), ignition pickup not reading correctly (incorrectly positioned), secondary throttle servo not opening the secondaries correctly, etc.

Some of that I would THINK would throw some error codes, but.... is possible they might not.....


and this I should have asked earliest probably - was the bike running fine for a while AFTER the build, and suddenly started acting up, or was the bike like this IMMEDIATELY after the build? If the latter case is true, it never worked right after the build, I'd be wondering a lot more about whether a mistake was made in build or setup.....

Also, you are in England? I'm in the US, dont work on euro market bikes, but I DO always read about them having immobilizers fitted from stock, and have HEARD sometimes they can act up, cause some issues....... Esp with revving to a certain point and cutting out. *shrugs* i dunno, just mentioning I've heard of some issues.....

Premium Member
2,086 Posts
Sorry for the double post, but I re-read your original post and found something worth mentioning

I highly doubt its a charging system issue. If the battery is fully charged, the bike will run for a little while with NO charging system. Half hour or so, maybe 45 minutes (with no headlights, and i'm presuming you dont have any giving you are racing it, unless maybe you are running night time endurance events, and if so, fucking cool!)

Anyways, the performance might start to drop off a bit near the end as the voltage runs down, but that would be a few HP. Maybe right at the end it would run crappy, but only at the end. Up till then, it would be running fine.

So I highly doubt that issue is causing your problem. If you wanted a bit more reassurance, since you already checked the charging system at idle, you could always check it with the bike warmed up, on a stand, engine in neutral, and run it at 5,000 rpm and check voltage at battery. If you're getting 14.5-15.5 at battery, with decently charged battery, you dont have a charging system issue. But like i said, I dont think a charging system issue would cause your problems

One time, I was working on my heavily built K4, doing a bunch of work to it and then took it to the dyno. It ran for about 20 minutes on highway, and then ran on dyno for a bit. There were a couple of times we started and stopped it, and at some point the starter begain to run slow

Thats when i realized i had forgotten to plug the stator in! (I had unhooked it for access to some other wiring / parts that were nearby)

Up until then, i simply didn't even notice, and it wasn't evident, that it wasn't charging (and with the stator unhooked you will get NO charging, by definition!)

I wouldn't suggest anybody try the same, but just goes to show you what can happen.... or doesn't.....
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