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Discussion Starter · #1 ·
Hi Everyone,
Bit of history RD07A 1996, owned since 2000. Bike has been off road (was all working) for the last 10 years.
Revived recently and cleaned tank ( very rusty) changed plugs, air filter, oil, fuel filter, coolant, brakes and had the carbs ultrasonic cleaned.
Started first time and ticks over and revs cleanly through the range in neutral.
On a run the bike runs well up to about 2800 - 300 rpm and then starts to stutter and will not pull any higher.
I have changed the rubbers between head and carbs, cleaned and sealed rubbers between carbs and airbox and checked all air vent hoses.
Now I am a bit stuck,
Any advice greatly appreciated.
 

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It is possible the fuel pump is not getting enough fuel through at higher revs when more is needed, when riding. I would check this out by by-passing the pump. The fuel should get to the carbs by gravity so long as the fuel level in the tank is above the float bowls, which roughly equates to a tank at least half full. If the stuttering continues it will rule out the pump as the culprit. Alternatively, measure the pump's fuel flow in litres per minute to see if it equals the recommended minimum (which is given in the Haynes manual) - that's quite simple to do by disconnecting the fuel pipe on the carb side of the pump and placing a measuring jug under it. Once the pump (a not uncommon cause of fuel starvation, particularly the OEM one) has been ruled in or out, you can move onto further tests as necessary.
 

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Discussion Starter · #5 ·
It is possible the fuel pump is not getting enough fuel through at higher revs when more is needed, when riding. I would check this out by by-passing the pump. The fuel should get to the carbs by gravity so long as the fuel level in the tank is above the float bowls, which roughly equates to a tank at least half full. If the stuttering continues it will rule out the pump as the culprit. Alternatively, measure the pump's fuel flow in litres per minute to see if it equals the recommended minimum (which is given in the Haynes manual) - that's quite simple to do by disconnecting the fuel pipe on the carb side of the pump and placing a measuring jug under it. Once the pump (a not uncommon cause of fuel starvation, particularly the OEM one) has been ruled in or out, you can move onto further tests as necessary.
Thank you, I will give both of those a try. I was also going to check the chokes as well.
Will report back.
 

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If it revs cleanly under 3000rpm, it's unlikely to be the choke(s), as if the chokes were stuck on after the engine had warmed-up it would be running rich and would not rev cleanly. But probably worth checking. Some owners, me included, have disabled the chokes so they're permanently off and thus the risk of them getting stuck is negated. I think the 07A must run a bit rich as standard, at least on the slow running circuit, otherwise it would not start without the chokes, particularly in colder weather. There's a slight knack to starting when cold, which involves fractionally opening the throttle just as it begins to fire-up. In many years of not using the chokes, it had never failed to start, even in freezing weather.
On the other hand, my older RD04 always needs some choke when the engine is cold, all year round. The carbs are different to the 07 and clearly are not rich as standard on the slow running (pilot) circuit.
Possibly the reason why the engine revs over 3000rpm when in neutral is for this reason.... when in neutral, I assume the engine's been idling at tickover speed at which point the fuel requirement is less and the float bowls fill up. When then revved over 3000, there's enough fuel in the bowls to let it rev over 3000 for a short period, maybe say up to 30 seconds. If you kept the revs over 3000 in neutral for over the hypothetical 30 seconds, it may well start to die, as the fuel in the float bowls is used up more quickly than it can be replenished. Anyway, good luck with the detection.
 

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Discussion Starter · #7 ·
Update. I tried bypassing the pump and also replaced the fuel pump with a new Faucet fuel pump, no change as it still stutters at 3000rpm when ridden.
Revs cleanly in neutral on the stand.
What next, advice appreciated.
Thank you.
 

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Are Jets correct for the model? Has exhaust been changed? (Fulleing will be diffferent). What numbers do you have for Main Jets?
It may well pull okay up to a point, but then fuelling isn't enough... so maybe richer set required. Did you ever rev it and have this issue 10yrs ago?

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Discussion Starter · #9 ·
@Bardley Thanks for your reply. Never had any issues in the past. Everything is standard. Might remove the carbs and have them cleaned again and can check the main jets.
 

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When you say it revs cleanly in neutral on the stand, does it rev cleanly all the way up the rev range? And for how long.... say you keep the revs at 3500 or so, will it rev cleanly indefinitely or do you just rev it momentarily and then let it go back lower revs/tickover? What happens if you put it in gear on stand and then rev up to over 3000rpm - does it stutter like you say is does when riding it?
 
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