tony_walsh Posted September 14, 2008 Share Posted September 14, 2008 Can anyone tell me why the power can be sluggish to come on when required? Why would the tiny tack show revs of 9000 and when the caliper is pressed all the way home the power fall back a thousand or so revs and become eratic in output. I expect the revs to come on when I want and continue until I ease off on the throttle. Quote Link to comment Share on other sites More sharing options...
Guest Posted September 14, 2008 Share Posted September 14, 2008 possibilities are long wrong carb ajustment bad plu air getting in the head or the carb worn rings cracked piston is the revs eratic or is it not on full revs when you aply full revs also when you aply full revs do you get them and then they drop and come back or drop and you dont get them at all but it is ok on low revs? Quote Link to comment Share on other sites More sharing options...
tony_walsh Posted September 14, 2008 Author Share Posted September 14, 2008 possibilities are long wrong carb ajustment, bad plu, air getting in the head, or the carb' worn rings' cracked piston, is the revs eratic or is it not on full revs when you aply full revs also when you aply full revs do you get them and then they drop and come back or drop and you dont get them at all but it is ok on low revs? Answer If I apply the throttle slowly the revs come on and even reach 9000 + but then fall away alarmingly. I then have to throttle back and coax them back again before it happens again. The engine seems to run well on low revs and on idle it ticks away. This is a new carb. Bye the way what is a plu? I am new to 2-strokes and I can see it is going to be a steep learning curve. Quote Link to comment Share on other sites More sharing options...
gordon_dunn Posted September 14, 2008 Share Posted September 14, 2008 I've had this before- and recognise the symptoms..... it's an easy cure. Just remove the back plate off the carb and clean the internal filter behind the membrane- you should do this every 15hrs or so, even if you are using fuel filters and a a 'Mr.Funnel' fuel separator. You'll be surprised what comes out of the filter. I've got a procedure document- (illustrated) Please let me know if you want it. gd Quote Link to comment Share on other sites More sharing options...
Guest Posted September 14, 2008 Share Posted September 14, 2008 it was a miss spelt word it should have been plug lol sorry, and the other chap that has replied has a good conclusion also cracked diaphram , it hink the carb is the starting point with it to be honest two strokes are simple very simple and not expensive to sort Quote Link to comment Share on other sites More sharing options...
gordon_dunn Posted September 14, 2008 Share Posted September 14, 2008 Here's the cleaning procedure for the carb- Use your flightlog to schedule this procedure at least every 15hours, and you'll never be caught out again. It's also a good opportunity to give the rest of the carb/intake system a good inspection. This does not just apply to H&E machines- most equipment with a Walbro will have the same characteristics. It may seem a little inconvenient, but debris being trapped in this filter is better than stuff entering the internal areas of the carb. Link as follows- http://www.gordondunn.co.uk/forumdownload/H&E%20R80.pdf GD Quote Link to comment Share on other sites More sharing options...
pete_b Posted September 14, 2008 Share Posted September 14, 2008 I've had this before- and recognise the symptoms..... it's an easy cure.Just remove the back plate off the carb and clean the internal filter behind the membrane- you should do this every 15hrs or so, even if you are using fuel filters and a a 'Mr.Funnel' fuel separator. You'll be surprised what comes out of the filter. I've got a procedure document- (illustrated) Please let me know if you want it. gd I agree I had this as well Pete b Quote Link to comment Share on other sites More sharing options...
paramotormike Posted September 15, 2008 Share Posted September 15, 2008 I had this problem too. It turned out I had depressed the primer on the carb to hard and had bent it slightly. This stopped me getting power at the top end. Open the front part of the carb (4 screws I think) ans check it looks good, and not bent) Mikey Quote Link to comment Share on other sites More sharing options...
dantheman Posted October 21, 2008 Share Posted October 21, 2008 I have this problem now, fitted a replacement diaphragm kit hoping that was the problem but unfortunately it's not. I also removed the gauze filter and cleaned it (was clean anyway) and removed the fuel & mixture needles to clean out the jets. Starts and idles fine, revs fine to 3/4 throttle but dies away when you nail the throttle wide open, high screw makes no real difference. Fuel pump puts loads of fuel into the carb when squeezed, I'm positive there is no blockage in the fuel line so it's surely still the carb ?? ideas anyone please ?? I'm tempted to bend up the needle valve lever as Mike mentioned..... Quote Link to comment Share on other sites More sharing options...
Guest Posted October 21, 2008 Share Posted October 21, 2008 If you remove the needle valve, give it a good clean and then flick it into a field of long grass in the hope you never see it again... Repeat this process until you have nothing left. SW Quote Link to comment Share on other sites More sharing options...
paramotormike Posted October 21, 2008 Share Posted October 21, 2008 I think that there was also an issue with the primer bulb. If your fuel leaks back into the fuel tank very fast, it may be the primer bulb has an internal leak. I had this problem and they sent me a new primer bulb set-up. After fitting the new one, the fuel would still be primed right up to the carb 2 or 3 days later. If yours returns to the tank after a few hours it might be worth a look. I seem to remember that the leak allowed air into the system only at high rpms. Hope this helps Mikey Quote Link to comment Share on other sites More sharing options...
Phil_P Posted October 21, 2008 Share Posted October 21, 2008 Consider a new plug too. My motor was coming up about 500 rpm short at full throttle. I fitted a new plug, and all the parts from the carb (Walbro 32) service kit bar the spring and valve (cos I didn't want to reset the pop-off pressure). This included three diaphragms and two filters plus all the gaskets. RPM's were immediately restored. NB there are two of the large oblong diaphragms supplied in the kit, made of different materials. I'm not sure of the differences although I understand the brown/grey semi transparent one is supposed to have a longer life. Those extra revs made all the difference to me getting off the ground. Quote Link to comment Share on other sites More sharing options...
dantheman Posted October 22, 2008 Share Posted October 22, 2008 Mikey - thanks for the tips, it looks like the hand pump primer bulb does not hold the fuel at all, you can't even pump fuel up out of the tank when the pipe to the carb is disconnected. Watch this space.... Quote Link to comment Share on other sites More sharing options...
Guest Posted October 22, 2008 Share Posted October 22, 2008 I flipping told you!!! Them hand primer jobs are just to much of a drain on the fuel draw. My RAD ran well, I then fitted a hand primer, and then it did not, I removed it and it did again. SW Quote Link to comment Share on other sites More sharing options...
dantheman Posted October 23, 2008 Share Posted October 23, 2008 Not so fast Simon, replaced the fuel primer and now fuel stays in the filter. However same problem exists, 3/4 throttle ok but WOT power dies away. Have tried bending up the meter lever to increase fuel flow which does richen it all up, makes it a sod to start but still dies away at peak. Running out of ideas now, am checking most things on the Walbro check sheet Quote Link to comment Share on other sites More sharing options...
Guest Posted October 23, 2008 Share Posted October 23, 2008 If all else fails, I know a lawnmower man who will 100% sort it out for you. SW Quote Link to comment Share on other sites More sharing options...
dantheman Posted October 23, 2008 Share Posted October 23, 2008 Am just testing the pop off pressure and it does seem quite high, roughly around 20 psi and sources say it should be around 10-12 so this may be part of the problem, however it's a spring cutting exercise to reduce the pressure and a one way modification. Here is a thought too, it's running a new prop which is 122cm (replacing a 125cm prop), what if the small decrease in diameter has given a slight increase in RPM which the motor has never been tuned for, it does run perfectly just before WOT with bags of power. Quote Link to comment Share on other sites More sharing options...
Guest Posted October 23, 2008 Share Posted October 23, 2008 Dan, IIRC did you break a prop recently? Is this problem purely since you put a new prop on? If so can you please tell us the diameter and pitch of the prop before and the prop you have now. Also if you have a CHT indication have the temps started to increase? Quote Link to comment Share on other sites More sharing options...
Guest Posted October 23, 2008 Share Posted October 23, 2008 Just seen the post you made while I was preparing mine! The diameters are not going to make a huge difference but the pitch difference could be vital. Quote Link to comment Share on other sites More sharing options...
dantheman Posted October 23, 2008 Share Posted October 23, 2008 You are correct, symptoms appeared when new prop was attached. The new prop at 15" out from the centre, the angle of attack is approx 21 degrees which I believe equates to 36" of pitch. The old prop (49x30R) was 30" Quote Link to comment Share on other sites More sharing options...
Guest Posted October 23, 2008 Share Posted October 23, 2008 Bingo, there's your answer. That is massively overpitched. Your old prop would have been just under 18 degrees. The Black Devil props that ConAir sell are also in my opinion overpitched and give exactly the same results (as also discovered by Indigo Miles). The engine initially spins up to full revs but after a few minutes it can't sustain the rpm and they drop down while the CHT goes through the roof. Send that prop back for a refund. By the way a Ros 125 with a similar diameter and reduction runs a 29" prop so 36" is way out. Where did you buy the prop from and did they claim it was correct for an HE R120? I think I suspect I may know already but I am curious to see if I'm right! Quote Link to comment Share on other sites More sharing options...
dantheman Posted October 23, 2008 Share Posted October 23, 2008 Manchester Paragliders sell it as a P12 122cm. Surely too much pitch would bog the engine down and not reach max RPM ? PROP PITCH CALCULATOR LINK Quote Link to comment Share on other sites More sharing options...
pete_b Posted October 23, 2008 Share Posted October 23, 2008 Manchester Paragliders sell it as a P12 122cm. Surely too much pitch would bog the engine down and not reach max RPM ?PROP PITCH CALCULATOR LINK Your right Dan unless it is slightly over pitched then it will run full chat and then die back a little if it very over pitched then it will only run up to a certain rpm (mine will only run up to 6500 as it is deliberately over pitched). Why would the EGT go through the roof?? (unless your mixture is out) Pete b Quote Link to comment Share on other sites More sharing options...
Guest Posted October 23, 2008 Share Posted October 23, 2008 Just as I thought! I've had 2 props from them supposedly for a Black Devil and a Ros 125 and both of them have been more than 5 degrees out of pitch. They are made by TP out in Thailand who copy any old prop and if the original owner says it will work on any particular type then they will sell it as suitable for that type! Overpitched props will spin up to high rpms before eventually getting bogged down. My BD would maintain full power (7500 rpm) for about 5 minutes (ie enough time to get airborne and climb out) before then it wouldn't go above 6400rpm. Fortunately my CHT gauge would tell me it was time to throttle back and land. It took me several months of chasing the carb before I worked out it was a pitch issue. A change of prop and it was a whole new machine! This is one of the reasons why I completely endorse the ground adjustable GSC propeller and am currently in discussions with Rick to make an adapter to allow Top 80, Ros and HE motors to run reversive versions on their 4 bolt M6 60mm PCD hubs. On the plus side, Paul Kilburn is very good at taking props back! Quote Link to comment Share on other sites More sharing options...
pete_b Posted October 23, 2008 Share Posted October 23, 2008 Just as I thought! I've had 2 props from them supposedly for a Black Devil and a Ros 125 and both of them have been more than 5 degrees out of pitch. They are made by TP out in Thailand who copy any old prop and if the original owner says it will work on any particular type then they will sell it as suitable for that type!Overpitched props will spin up to high rpms before eventually getting bogged down. My BD would maintain full power (7500 rpm) for about 5 minutes (ie enough time to get airborne and climb out) before then it wouldn't go above 6400rpm. Fortunately my CHT gauge would tell me it was time to throttle back and land. It took me several months of chasing the carb before I worked out it was a pitch issue. A change of prop and it was a whole new machine! This is one of the reasons why I completely endorse the ground adjustable GSC propeller and am currently in discussions with Rick to make an adapter to allow Top 80, Ros and HE motors to run reversive versions on their 4 bolt M6 60mm PCD hubs. On the plus side, Paul Kilburn is very good at taking props back! Just order a blank hub and drill it/get it drilled to fit your motor. Petye b Quote Link to comment Share on other sites More sharing options...
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