Won't rev past 6k

Forum rules
Please can you post items for sale or wanted in the correct For Sale section. Items / bikes for sale here will be removed without warning. Reasons for this are in the FAQ. Thanks
evoluzione750
Settled in member
Reactions:
Posts: 25
Joined: Sun Jan 18, 2015 12:55 am
Bike owned: NC27, 3EN1, GK75A, NC29
Location: Oxfordshire, UK
Won't rev past 6k

Post by evoluzione750 » Sat May 09, 2015 7:06 pm

The 3EN1 is giving me a hard time, as it will not tach up past 6k and won't hold an idle. The bike starts up pretty easy, give it at least half choke when stone cold and it fires right up.

When I bought it, the chap said the motor had been rebuilt recently, which I can see that it has a few new parts and fresh RTV, so I had reason to believe him. He thought the stator might be bad as the battery goes flat after riding for a while, and he replaced the R&R hoping that would solve the problem. I tested the stator itself for continuity and it seems just fine, no shorts, and after firing the bike up and putting a meter across the battery terminals, it reads about 13.8 V at idle (what I can get close to anyways) and only raises to 13.9 at about 5k. I always thought it was supposed to be generating above 14 V running, so I think there might just be a draw somewhere in the electrical system.

The carb settings when I opened it up were the needles all in the position second from the top and float heights of 25.0mm, 25.0mm, 24.5mm, and 24.2mm, idle air screws at 1&1/8 turns out, 1&1/2 turns out, 3&1/2 turns out, and 3&1/2 turns out going from cylinders 1-4. The diaphragms seem to be in good enough shape, no holes that I could see.

Taking the plugs out, cylinders 1-3 all looked like it was running rich, with cylinder 4 looking much leaner. It turns out that plug #4 was only turned in about 1/4 of the way in due to mangled thread, which I have since fixed. I just put brand new plugs in to see if it makes a difference, which it hasn't.

I've had the carbs off and hosed down the innards with carb cleaner and resent the float heights to 22mm (that's what I've read somewhere on the forum before, please correct me if I'm wrong) turned the idle air screws to 2&1/2 turns out and that made no difference whatsoever.

To the best of my knowledge, the bike is completely stock. If I can get it to hold an idle, I'll give the carbs a balance and see if that affects anything. I don't know if the issue is electrical or just carburation, but it's been driving nuts because the weather is perfect and I'm stuck staring at a bike in pieces because I can't figure out what is probably a simple problem.

Any ideas? Thanks

Evilchicken0
Site Supporter
Site Supporter
Reactions:
Posts: 9490
Joined: Tue Apr 29, 2008 8:59 pm
Bike owned: Bimota SB6 Yamaha FZR 3TJ x2
Location: Lundin Taan
Re: Won't rev past 6k

Post by Evilchicken0 » Sun May 10, 2015 12:39 am

The voltage is low it should come up to about 14.5 volts.
The main jets come in at 6,000 rpm ... could the idle and main jets have got crossed over ?
Make sure the exup opens and closes.

evoluzione750
Settled in member
Reactions:
Posts: 25
Joined: Sun Jan 18, 2015 12:55 am
Bike owned: NC27, 3EN1, GK75A, NC29
Location: Oxfordshire, UK
Re: Won't rev past 6k

Post by evoluzione750 » Mon May 11, 2015 7:00 am

The exup seems to be working, resets itself when turning the run switch on. With the chrome cover off, I've verified it is free.

If the main jets occupy the spot closest to the idle mixture screw, the starter jet next to it, and the idle jet in the recess,then they are all in the correct spots. It has 97.5 mains, and I believe 52.5 starter (they're all chewed pretty well, it's hard to make out the numbering), and the idle jets are chewed to smithereens, so I haven't been able to extract them, let alone make the numbers out.

While searching for other possible culprits, I thought I'd give the ignitor box a look. The box has 2 connectors on, one with 8 pins and the other with 6. The leads connecting to the box on the bike only have 7 wires going into the 8 pin connector and 5 going into the 6. I've read something along the lines that the ignitor limits the speed of the bike to something like 170kph through a circuit coming from the speedo going into the ignitor box, and if attempting to derestrict it by removing the circuit, it activates a lockout that prevents the engine from turning over a certain engine speed. I thought it sounded kind of like what was happening to mine; it doesn't cut out or sputter, it just holds steady at about 6k even with WOT.

A 3EN1 wiring diagram seems to be a bit of a unicorn though, so I don't know if my suspicions are true. Is this derestriction fairly common, or does the ignitor only need 12 out of the 14 pins on offer?

Image

Image

Evilchicken0
Site Supporter
Site Supporter
Reactions:
Posts: 9490
Joined: Tue Apr 29, 2008 8:59 pm
Bike owned: Bimota SB6 Yamaha FZR 3TJ x2
Location: Lundin Taan
Re: Won't rev past 6k

Post by Evilchicken0 » Mon May 11, 2015 1:22 pm

I don't think it's cdi related, usually the cdi will restrict to 12,500 rpm if you mess about with it ... don't try to do a home derestriction.
So I reckon it's the carbs ... I think Will would be better placed to comment on the details of this. Maybe download and have a look at a 600 3HE manual, it should give the carb jet positions.
There is a slightly cryptic ebay add http://www.ebay.co.uk/itm/Yamaha-FZR-40 ... 2a506802a7 Ask him the model of FZR, and/or a picture of the CDI - the model is on there. You could swap out these carbs for the ones in the add and know they work.

evoluzione750
Settled in member
Reactions:
Posts: 25
Joined: Sun Jan 18, 2015 12:55 am
Bike owned: NC27, 3EN1, GK75A, NC29
Location: Oxfordshire, UK
Re: Won't rev past 6k

Post by evoluzione750 » Mon May 11, 2015 10:21 pm

I'll definitely have a look at a 600 manual. I've taken the carbs apart again and made sure every passage is completely free using carb cleaner and compressed air. They all seem free to me, so the only thing left is a balance.

The ebay ad does seem a bit shady, but I'll message him. Should the carbs off an earlier model theoretically work, just swap the jets?

evoluzione750
Settled in member
Reactions:
Posts: 25
Joined: Sun Jan 18, 2015 12:55 am
Bike owned: NC27, 3EN1, GK75A, NC29
Location: Oxfordshire, UK
Re: Won't rev past 6k

Post by evoluzione750 » Tue May 12, 2015 2:41 am

Are there seals (square rings is what I've read they're called) that goes beneath the main jet in the jet housing? None of the mains had any. I probably sound a bit daft, but my previous bikes never had these, so I didn't know they needed to be there.

Image

Evilchicken0
Site Supporter
Site Supporter
Reactions:
Posts: 9490
Joined: Tue Apr 29, 2008 8:59 pm
Bike owned: Bimota SB6 Yamaha FZR 3TJ x2
Location: Lundin Taan
Re: Won't rev past 6k

Post by Evilchicken0 » Tue May 12, 2015 1:07 pm

I don't think mine had any either
The carbs look clean to me

willandrip
Site Supporter
Site Supporter
Reactions:
Posts: 1223
Joined: Sun Aug 14, 2011 8:33 am
Bike owned: Far, far too many now
Location: North Tyneside Tyne and Wear
Re: Won't rev past 6k

Post by willandrip » Tue May 12, 2015 5:32 pm

No O ring type seals under the jets.

There is a 3EN2 (same carbs) parts fiche in the documents section.
A red box doth not a Snap On make.

evoluzione750
Settled in member
Reactions:
Posts: 25
Joined: Sun Jan 18, 2015 12:55 am
Bike owned: NC27, 3EN1, GK75A, NC29
Location: Oxfordshire, UK
Re: Won't rev past 6k

Post by evoluzione750 » Tue May 12, 2015 9:51 pm

Darn, I was hoping that would be it. Each of the main jet circuits is clean as whistle now, and nothing else looks out of the ordinary. The last thing I can think to do is a valve clearance check.

willandrip
Site Supporter
Site Supporter
Reactions:
Posts: 1223
Joined: Sun Aug 14, 2011 8:33 am
Bike owned: Far, far too many now
Location: North Tyneside Tyne and Wear
Re: Won't rev past 6k

Post by willandrip » Tue May 12, 2015 10:37 pm

I had to get a parts manual out..........

I think your mains are 92.5 (the numbers are hard to read) for the outer cylinders anyhow and should be 90s for the inner cylinders.

That difference would not cause your symptoms if they are indeed 97.5s.


Try leaning out the needles before buying new jets.... if it helps then buy the jets.....Gawd knows if the PO cleaned them with a drill bit if the heads are chowed up as you state.



On the electrical side...... I have run them with a totally jiggered battery after removing jumper leads once started
and the motor misfires chronically. (I don't think its that)

If it starts easily ,it's not valve clearances.

Are the chokes returning properly ?

Have you verified that you float height setting equates to the fuel level setting using the line on the carb body, a piece of 6mm bore clear tube from the bowl drain and the correct height measurement ? Bike needs to be upright.

Some of the pins are blank on the TCI plugs......as Boris states; it's not the restriction circuit.
A red box doth not a Snap On make.


Post Reply