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PostPosted: October 10, 2008, 7:26 am 
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So we just got our Sr7 running under it's own power. Everything is great except in first gear and sometimes 2nd and sometimes while shifting into 3rd, the car is very jumpy. It will lift the back tires off the ground while in first while just tooling around. It's like when in a car with a manual trans you acclerate in 1st then let off and let the engine brake the car. Just before it's stalls it jumps(only word that i can think of). Except it's quite bad. We're thinking of just using 2nd even 3rd and up. The only problem is it has done this while shifting from 2nd to 3rd while under load. It's a little scary to say the least. I assume this is because of the motors small flywheel and the increase in load on it. It would mean that it engine brakes quicker then in the bike. Is this right?

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 Post subject: Sounds like axle hop
PostPosted: October 10, 2008, 7:56 am 
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From your description?, It sound like axle hop. The rear trailing arms need to be parallel at static ride " no anti-tramp" and you may have to high of a rear spring rate. Also if the rear shocks damping is adjustable, try reducing it. start at the lowest setting and work up. The other thing is a high sprung Wt. and rotational mass, but that is difficult to fix $$$.

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PostPosted: October 10, 2008, 9:41 am 
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Are you running one of those "guibo" or whatever thingys?

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PostPosted: October 10, 2008, 10:49 am 
Sounds to me like maybe the rear end is binding up somehow, kind of like when you lock the hubs on a 4X4 and try to steer it don dry pavement. If it seems like that's what it's doing, I'd check that the radius arms are adjusted so there's no binding through the range of movement of the rear end, and that there's no too much "anti-squat" dialed in...


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PostPosted: October 10, 2008, 12:00 pm 
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Try this. Put the car on jackstand and remove the wheels and shocks, supporting the uprights at ride height. Now, lift - by hand - the upright; if it can't be easily lifted 2-3" (or whatever your suspension bump travel is) it is binding. As alluded to above, this typically happens when trailing arms aren't the exact same length and/or rubber bushings aren't used to take up the difference.

Or, is what you're describing actually this: the gas pedal is so sensitive that when you touch it, the car accelerates so quickly that your foot comes off the throttle. Then the car slows down so fast that you (and your right foot) slump forward, back on the gas. The process repeats itself over and over, giving what you're describing. If that the case you need to rework the throttle linkage to greatly decrease the sensitivity of throttle application.

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PostPosted: October 10, 2008, 6:26 pm 
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It does seem somewhat like too sensitive of a throttle but I'm not sure that it is. We are using the stock throttle cable and there is about 2'' of stroke on the pedal. By radius arms do you mean the lower control arms? Our car has IRS and I'm not sure which is the radius arm. The axles move smoothly up and down. Here's a lil vid of what it's doing. It's like it's wheel hoping but while slowing down. The shocks are max soft and springs seem to be about right. I'll check the alignment etc. and see if that helps.

http://www.flickr.com/photos/30221154@N07/2929523995/
It's at the end of the vid.

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PostPosted: October 10, 2008, 7:00 pm 
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I think that can be tested for by putting a stop under the gas pedal, at the point where the problem occurs. Then take the car out and keep your foot all the way down so the throttle stays fixed at one point. Does it happen then?

Oh, does it happen when you take your foot completely off the pedal?

Another thing it could be is if the engine rocks at all, it may be pulling on the throttle such that it gives itself gas then cuts off, rocking back and forth.

Just some ideas.

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PostPosted: October 10, 2008, 7:03 pm 
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The engine is mounted solidly. Its like the clutch and rear end aren't at the same speed. I should try feather the gas and see if that helps.

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PostPosted: October 11, 2008, 1:03 am 
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Bolt that camera where we can see the driveshaft and engine and repeat. :)

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PostPosted: October 11, 2008, 1:39 am 
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Dirt or partial blockage in the fuel system?


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PostPosted: October 11, 2008, 9:05 am 
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I would watch the carb end while working the throttle pedal. Look for sticking or slow movement when releasing the pedal.

You probably have a single, automotive type throttle cable, a spring in addition to the carb end spring, and no quadrant (arc'd channel) for the cable to ride in. Usually on bikes, there are two throttle cables that work against each other. The only spring is the one on the carb end.

The stock handle bar twist throttle has a lever arm of about 1 inch from the pivot point. Moving the cable connection on the pedal end more than 1 inch from the pivot point would make the pedal more sensitive than stock if the carb end is stock.

The quadrant is like a cam lobe controlling the pedal to carb arm ratio. A quadrant that stays the same distance from the pivot would have a consistent rate of cable pull from idle to full throttle. A simple lever with no quadrant has a decreasing rate of cable pull from idle to WOT.

IMHO, the preferred set up would be a quadrant that gets further from the pivot as the throttle is opened. It would be less sensitive near closed throttle (when you want to be smooth) and more rapidly apply full throttle. Also, pedal travel would be less compared to a simple lever.


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PostPosted: October 11, 2008, 9:37 am 
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I noticed the bike has two throttle cables. We are using the spring setup on the throttles and an aditional return spring mounted to the throttles. The main purpose of this spring is to provide some resistance(feel) in the pedal. The throttles return fine by themselves. I have no idea what a quadrant is. I'd assume it's a linkage setup that similar to what's found on car carb's that helps with smoothening the procedure.

Just had the car out this aft for a bit. I think most of the problem is learining how to drive it smoothly. I had allmost no problem today driving it did run out of gas though.

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PostPosted: November 30, 2008, 1:03 am 
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Miatav8,MstrASE,A&P,F wrote:
I would watch the carb end while working the throttle pedal. Look for sticking or slow movement when releasing the pedal.

You probably have a single, automotive type throttle cable, a spring in addition to the carb end spring, and no quadrant (arc'd channel) for the cable to ride in. Usually on bikes, there are two throttle cables that work against each other. The only spring is the one on the carb end.

The stock handle bar twist throttle has a lever arm of about 1 inch from the pivot point. Moving the cable connection on the pedal end more than 1 inch from the pivot point would make the pedal more sensitive than stock if the carb end is stock.

The quadrant is like a cam lobe controlling the pedal to carb arm ratio. A quadrant that stays the same distance from the pivot would have a consistent rate of cable pull from idle to full throttle. A simple lever with no quadrant has a decreasing rate of cable pull from idle to WOT.

IMHO, the preferred set up would be a quadrant that gets further from the pivot as the throttle is opened. It would be less sensitive near closed throttle (when you want to be smooth) and more rapidly apply full throttle. Also, pedal travel would be less compared to a simple lever.


Agreed 100 percent. Being from the bike world he is exactly right. On a bike the ratio of the throttle bodies opening becomes smaller as you twist the trottle in a linear speed (equal throughout).

Think of a cam lobe. When you first start twisting the throttle the radius is small. As you twist it more the radius of the lobe that the cable rides on increases in radius.


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PostPosted: December 3, 2008, 9:58 pm 
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Ideally a setup like on a holley carb or something progressive linkage I think they call it would work well.

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PostPosted: February 19, 2009, 8:04 pm 
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After watching the posted video and rethinking what is actually happening I think you are experiencing a problem which is compounded by a few things. It seems to me you have a lurching which can happen with bike trannys. The dog type actuators have a certain amount of backlash which can allow the driveline to windup and cause a clunking lurching action. I had the same problem with my SR7 at first. A couple of solutions;
1. At low speed be really smooth coming off and getting back on the throttle. Even having your seatbelts as tight as poss and bracing your throttle foot on the tunnel helps to reduce it. It still happens sometimes to me and the only way to totally eliminate it is to stab the throttle or push the clutch in. Slow intersections cause this condition the most.
2. If under low throttle inputs the fuel inj system is a little lean this situation will be very magnified. Do you have a piggy back system? If yes try to richen the low speed ratio.
3. If you have a reverse box inline with the prop shafts you may run into driveline angle problems that will cause this to be wildly magnified. Hayabusa SR7s have the output shaft far over to the right side and any setup other than stock causes steep driveline angles. I had to use a propshaft with double cardan joints at both ends because traditional u-joints would bind at such angles causing crazy driveline clunking at light throttle application.

Not sure if I am seeing/hearing what happened to me but those were the solutions for my car.


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