Jerry
09-29-2006, 10:38 AM
This question was on another forum, and I thought the answer would help others - as I've had this question several times before in PM's. Someone else had quickly answered with the advice that his midrange was too lean - and that he should attack the midrange. This isn't really accurate advice, as this engine the midrange is rarely used.....so here's the Q/A.
i`ve fitted this engine into my rappy 90 using 8.27 gearing , i`ve plumbed it as follows , exchaust to top of tank , fuel feed to pump , then to reg on carb , the problem is its getting so hot , and i mean hot , low end is half way , mid is abt 1.25 and top is 2.5 + , it splutters very badly on spool up but a dare not lean it out any more as i`m afraid it`ll seize up and all this on a normal curve as idle2 would in my eyes kill it , i`m using the century heli 20% juice , what am i not getting right , i`ve had a c-spec ps and that was fine , i`ve also read elsewhere that some people close the mid needle altogether , one last thing , once its spooled up its not to bad unless full throttle is used but then it bogs ( too rich ?) but when i land its very very hot , help!
On the SZ-PS the midrange is more of a supplement and is rarely required. Most of us are running with the midrange fully closed. OS changed the way the fuel is fed through the primary metering channel of this carb - in a way that more fuel is delivered over a broader range. Therefore, the midrange 'backdoor' is really not that much in demand.
To address the heating problem - it sounds to me like the sound you are describing is that horrible cackling, popping "im way to lean' sound. It probably spools pretty darn fast.
I understand why you are concerned. Ive also encountered this before - intermittently.
Every so often my PD07 would 'hang.' The overall effect was a cackly, quick spooling, too lean engine on startup/first spool.
Causes and fixes......
Believe it or not, I've gently tapped the pump case with a nicad glow driver or a screwdriver handle. (gentle but firm - i mean dont break the case....)
The pump is really just a couple chambers and 2 plastic flapper valves that move really fast and not very far. I think occasionally they can get hung up - either by magic or by a piece of small crud.
If you encounter what I'm describing - it is probably a pump issue. Try what I suggested.
The needles you described are insanely rich for this engine - so I think the PD07 simply isnt doing its job.
This is all assuming your fuel tank/plumbing is perfect, all headbolts are tights, no holes in plumbing, a functioning regulator - a carb thats bolted down, an engine that is really attached to it's drivetrain, a fan that is actually blowing air, glowplugs that are really screwed in, and at least the factory shimming in the tank , and that you are running a brand name fuel between 15-30%nitro content.
Jerry
i`ve fitted this engine into my rappy 90 using 8.27 gearing , i`ve plumbed it as follows , exchaust to top of tank , fuel feed to pump , then to reg on carb , the problem is its getting so hot , and i mean hot , low end is half way , mid is abt 1.25 and top is 2.5 + , it splutters very badly on spool up but a dare not lean it out any more as i`m afraid it`ll seize up and all this on a normal curve as idle2 would in my eyes kill it , i`m using the century heli 20% juice , what am i not getting right , i`ve had a c-spec ps and that was fine , i`ve also read elsewhere that some people close the mid needle altogether , one last thing , once its spooled up its not to bad unless full throttle is used but then it bogs ( too rich ?) but when i land its very very hot , help!
On the SZ-PS the midrange is more of a supplement and is rarely required. Most of us are running with the midrange fully closed. OS changed the way the fuel is fed through the primary metering channel of this carb - in a way that more fuel is delivered over a broader range. Therefore, the midrange 'backdoor' is really not that much in demand.
To address the heating problem - it sounds to me like the sound you are describing is that horrible cackling, popping "im way to lean' sound. It probably spools pretty darn fast.
I understand why you are concerned. Ive also encountered this before - intermittently.
Every so often my PD07 would 'hang.' The overall effect was a cackly, quick spooling, too lean engine on startup/first spool.
Causes and fixes......
Believe it or not, I've gently tapped the pump case with a nicad glow driver or a screwdriver handle. (gentle but firm - i mean dont break the case....)
The pump is really just a couple chambers and 2 plastic flapper valves that move really fast and not very far. I think occasionally they can get hung up - either by magic or by a piece of small crud.
If you encounter what I'm describing - it is probably a pump issue. Try what I suggested.
The needles you described are insanely rich for this engine - so I think the PD07 simply isnt doing its job.
This is all assuming your fuel tank/plumbing is perfect, all headbolts are tights, no holes in plumbing, a functioning regulator - a carb thats bolted down, an engine that is really attached to it's drivetrain, a fan that is actually blowing air, glowplugs that are really screwed in, and at least the factory shimming in the tank , and that you are running a brand name fuel between 15-30%nitro content.
Jerry