Bike wont rev out....

M

mizike77

Junior member
Hi All,
My Jota America 1200 will not rev cleanly. This is a project bike that sat for a few years when I got it. I did not ride it before I did a few modifications to it, so I did not know if this issue was there before or not.
This winter I :
Completely rebuilt carbs 60 idle 115 main 70 starter otherwise stock internals
Replaced intake orings
Replaced choke plungers
fitted 4C cams
shimmed valves
Put a Laverda racing 3 into 1 on it ( yes I know this is not the ideal pipe)
Installed short velocity stacks

I also did much other work that does not apply to the engine.
When I set cam timing I used the recommend specs from the Laverda mania web site .

The bike will start very easily and Idle all day. It takes throttle beautifully while on the lift . Very crisp and quick. All sounds and feels great. That is until I went for my first test ride yesterday. At anything over 1/3 throttle the bike drops off and is not happy until I roll the throttle back . It is as if I am out of fuel or hitting a rev limiter. This coincides with around 4k rpm .
I ran out of time last night and will get back to it today. I need to do a plug reading and check ignition timing.
Are there any recommended ignition timing specs that will work well with my setup?
Thanks
 
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... first check the needle you use: K1 on middle position would be a good idea. 115 main is way to small if you go with 4/C, open stacks and open mega. Try a main jet 145-160. Ciao, Gert
 
main jet will not affect running at 30% throttle opening,

K1 needle (middle clip) and AB265 emulsion tube would be good (as Gert says)

as bike has stood,you may have fuel flow restrictions somewhere, start with the in tank filters on top of the pet cocks, even though you have cleaned the carbs, there may be crap in there somewhere, the float valves will need replacing to suit ethanol fuels (and this can be your cause of trouble as they may already be swelling if the old type) and 300 is a good size for your setup, the floats themselves may be the "white type" not the "black type" and the white ones do very often stick if not fettled correctly, causing a lack of fuel entry as well as too much of the stuff.

The trouble is it could well be electrics, when it falters you say it "comes back" if you roll off?, try this, at the 30% throttle faltering point, maintain that throttle position and see what happens, it it dies, becomes uncomfortable and you are judderring to a stop, then its probably not the carbs! but for some reason the spark is dying, what ignition system do you have and what maintenance have you doen to it?
CLEM
 
Your engine is running out of fuel because the mains are much too small for a 3/1 and open carbs in my opinion contrary to what writes my learned friend Clem.
Try 130.

Paul
 
I must say, I am not sure what ignition is in it. I would guess it is stock. Looking through the holes in the flywheel it has two banana coils on a plate. I have not fettled with the ignition yet.

I have new float needles and black floats.

I had both fuel taps off and apart. They should be clear.

My jetting is Wolfgangs recommendation .
 
Check the box under the tank or seat that supplies the wires to the coils.
If it's Bosch, it's OEM

Gerald
 
My Jota with a 3:1 was happy on 150 mains. A bit rich possibly but happy enough.
(Standard air box, 4C cams)
 
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Check with a strobe that it is advancing properly? As Clem says, 1/3 throttle is needle and needle jet which are metering your fuel, main jet comes into play from about 3/4 throttle and up, under that mj may as well not even be fitted. Put some registration marks on the twist grip so that you know precisely where 1/4, 1/2, 3/4 throttle positions are so that you are sure what part of throttle opening you are on. Can you use more throttle under 4000 and it pulls cleanly then goes pox at 4000? That is a symptom I have seen from dodgy ignition.
 
Don't rule out a problem with fuel tank venting until you examine it closely. When underway and the engine power drops off, open the filler cap. If the revs pick up, there's your problem. A vacuum in the tank is inhibiting fuel flow to the carbs.
 
Check the Ignition pickup wires, it is Bosch after all and the insulation falls off just like Ducatis. As the others have said 115 mains will be too lean with stacks and exhaust.
 
Similar problem here (1200 with 3/1) and I'm leaning towards it being too lean as well.

It's got Mikunis and the Czech box (all checked out OK on advance etc.) and running Dyna coils ... but still needs to be baby'd if you go for a big throttle opening. Not what you need over-taking at 100+
 
By all means, fit larger mains. But this issue is not related to your main jet. As previously pointed out, main jet operates from 3/4 to full throttle. And it is absolutely true, you can remove it and you will notice virtually no difference in running below 3/4 throttle. Sorry, Paul (and others), but you're wrong.
 
Got back to the bike today very briefly. Outer 2 plugs are dark and sooty. Didnt have time to get to the center. Looks like I have BTZ on mine. Put the timing light on real quick. Turned the idle up to 1200rpm . Had to turn the dial on my strobe to 10 to get it to line up the marks at 1200rpm. I twisted the throttle and though it was tough to look at the tach and the strobe at the same time it looks like it would advance at about 2500 rpm .
Now , I am admittedly not very good with timing. I am going by the green book and it looks like my numbers are not correct.
 
lavgert said:
... first check the needle you use: K1 on middle position would be a good idea. 115 main is way to small if you go with 4/C, open stacks and open mega. Try a main jet 145-160. Ciao, Gert
Click to expand...
Blimey. You must have different fuel in Europe than the stuff we get in Australia. Is it 50% alcohol?

My Jota had Dellortos with 140 mains in it when I bought it. It also had open intakes (air box but no filter in it) and a 3-1 exhaust with open mega. It was quite loud. It ran cleanly enough without any missing or coughing but was very fuel hungry and down on power. A dyno run revealed it to be maxing out 57 RWHP and way too rich at full throttle. After a few dyno pulls we ended up with 120 mains and something like a 10 HP gain in max power, and the air fuel ratio was looking much better although still a wee bit on the rich side, but I didn't have any smaller jets with me on the day. I reckon the factory got it right with 118 main jets.

The above was just the first step in getting it to run better. Next step was to chuck away the 3-1 and fit a set of (Redax) Jota pipes. That gained another 10 HP. A bit more fine tuning got it up to 80 RWHP which I suppose is about where it should be with a Jota spec engine. It still has the 120 mains in it. It also has double the fuel range than when I bought it, so it's running way more efficiently too.
 
1200 JOTA said:
Similar problem here (1200 with 3/1) and I'm leaning towards it being too lean as well.

It's got Mikunis and the Czech box (all checked out OK on advance etc.) and running Dyna coils ... but still needs to be baby'd if you go for a big throttle opening. Not what you need over-taking at 100+
Click to expand...
change your coils to Nology Pro-Fire, those Dyna coils have given me heaps of headaches
 
Providing your timing is on and Carbs to Spec - If your ride will not rev out (Pending your Exhaust system) - I would first suggest you go to a richer main Jet - Lest you lean out and melt a piston with too small of a main jet - Over Riched Jets are obvious as she floods out and fouls the plugs.

Going rich on the main jet is the safest and work down.

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This may be irrelevant in your case - Insure your Manifold Hose isn't leaking or collapsing.

Breganzies like a Strong Manifold Hose - Suggest Hydraulic quality and insure your Carb mounting gaskets are good and don't leak.

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Just saying something to CHECK - Safe Check for any engine ;o)

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PS: Ensure the Crank Case Ventilation isn't plugged !

Shit! It could even be related a dirty fuel delivery from the tank or the carbs can not flow air through the air filter your using - Start off with an open mouth Carb - You may not get any higher revs or Hi-End power then with open mouth Vs an Air Filter. My Dellorto VHB 30's never ran right with an air filter using 2 int 1 exhaust headers on my 70 750 SF - The solution may have been to mount VB 34 or 36's and use an air filter but the bike ran like a gang buster with open mouth 30's. I just changed my oil more often and never had issues.

Your engine may even have bad crank case or transmission seals.

With every thing thing done and checked twice my 70 Breganzie 750 SF was very capable of pulling strong to over 7800 rpm.

Just saying - Good LUCK with your Breganzie Moped ;o)
 
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