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Originally Posted by grizz1
(Post 4793277)
Are you sure your idle gap is correct ? Sounds like too wider idle gap being compensated by an overly rich LSN and lean HSN. Engine runs OK but will lean bog on a low tank and have that classic ¨load up idle¨ situation.
I may well be wrong, but the LSN tuning method I mentioned works very well for me. My 7 port runs awesome with great temps when tuned this way. |
Yes you should set the gap with no venturi in the carb.
The bottom of the venturi doesn't seal the carbs barrel so it's not correct to set the gap according to the venturi. Grizz1 even if the idle gap is wrong this doesn't explain the lean bog i experience. Of course your method is better in judging if the LSN is at least too Lean or too Rich since the load up metod depends on idle gap as well by altering the overall settings. When do you pinch the fuel line: -right after a WOT run -or after letting idle for some time(for how long?) |
Originally Posted by vti-chris
(Post 4793307)
Yes you should set the gap with no venturi in the carb.
The bottom of the venturi doesn't seal the carbs barrel so it's not correct to set the gap according to the venturi. I will reset the gap today and do the needles settings again. I will do report on evening. |
Hi vti - Warm up buggy fully first. Go for a good blast to clear everything out, then bring it in and pinch fuel line straight away. Adjust as needed, then go for another short blast and test it again until you get it right.
I´m certainly no expert, but I was taught this method by a couple of racers I know who are very experianced tuners. They combine this method with the clean take off method as a confirming test to ensure correct LSN setting. The lean bog - yeah ?? Most of the lean bog problems with the long lsn carbs was solved by setting the needles like I described at the bottom of my previous post (check that , as I added a couple of things as an edit). Chipo, set the idle gap like vti suggests. Maybe tune everything in with the original 8mm insert, then place your restrictor in when it´s all running good, then fine tune from there. It really does sound like an idle gap thing upsetting your tuning. |
Originally Posted by grizz1
(Post 4793277)
Hi Chipo - I think the key word is ¨significant¨ drop in RPM. If it just steadily gets slower and slower over time, not a problem. When it drops markedly after a short while, this is normally a sign that the LSN is too rich.
If you have a long LSN carb and your HSN is set at 1.25 turns in as you stated in a previous post, this seems way too lean on the HSN. That would be why your motor goes crazy when you lean the LSN. The HSN is like the water pipe coming into your house. It sets the total amount of water you can get. The LSN is like your tap. It sets what you get out of the tap when you open it. If you crimp your incoming water pipe (lean HSN) you won't get anything out of your tap (lean LSN) so thready rapid idle when you screw the LSN in. Are you sure your idle gap is correct ? Sounds like too wider idle gap being compensated by an overly rich LSN and lean HSN. Engine runs OK but will lean bog on a low tank and have that classic ¨load up idle¨ situation. I may well be wrong, but the LSN tuning method I mentioned works very well for me. My 7 port runs awesome with great temps when tuned this way. I have long needle carb. HSN 1/2 to 3/4 max in from flush. LSN 2 1/2 to 2 3/4 in from flush. Will run strong all day at these settings. How old is your engine? If it is new, or has less than 1 gal through it, it will lean bog if you run it even just a tad lean on the HSN when it´s still tight with the long needle. Read break in article on bottom of page 78 and tuning tips by MMods and Retro RC on page 131. Your idle will increase when you lean the LSN, thats normal. Get everything set for performance then lastly reduce the idle using idle screw if needed to where you want it. If I set my HSN 1/2 turn in from flush and LSN 2 1/2 turns from flush, my engine is without power, no top and no low. It gets too much fuel. Today I will set idle gap to 0.7 mm without venturi in carb. thanks for your time Grizzly |
vti - With the larger idle gap you find yourself setting the LSN very rich in order to get the idle speed correct. In effect you are flooding or loading up the engine to keep the idle where you think it should be (basically setting the idle speed using the LSN and not the idle screw). In order to get the motor running what appears to be normal, you must have quite a lean HSN, to restrict the flow of fuel to the LSN (because the LSN is set way too rich). With a full tank this situation is not great but it works and the motor will run OK but not to it´s full potential. However, when the tank level and fuel pressure drops you can´t get enough fuel pushed through the HSN at near to or WOT because you have the HSN closed off too much, hence your lean bog after a few minutes running.
Another tell tale sign of an incorrect idle gap and compensating rich LSN is your motor holding onto revs when jumping. |
Originally Posted by grizz1
(Post 4793336)
Chipo, set the idle gap like vti suggests. Maybe tune everything in with the original 8mm insert, then place your restrictor in when it´s all running good, then fine tune from there. It really does sound like an idle gap thing upsetting your tuning.
My idle gap was already set at only 0.55 mm. So Grizzly I'm not sure if the problem lies in to wide idle gap! Maybe is something with carb? Mine is exactly the same as here on the picture: http://www.massivemods.com.au/images/IMG_1684.JPG I will insert 8.0 mm venturi, set idle gap to 0.7 mm, set HSN 1/2 turn in from flush, set LSN 2 1/2 in from flush and go to our track, to try those settings again. |
For some reason my LSN only gets turned it about 1 full turn from flush and the HSN stays pretty close to flush. I broke the engine in leaner on the LSN at about 1.5 in. I have the new carb pictured above. Yesterday after racing I would bring it in for fuel and it would start to idle very erratic and almost shake the truggy. I keep thinking lean but with my settings I dont see how. I will have to check my idle because I realized I set it with the carb insert still in there. Also can anyone check their new carb with the airfilter off and see if the thin notch on the slide valve faces up toward the airfilter. Thanks
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Chedster - the notch is uppermost so it is visible looking down the carb throat.
Chipo - those settings are not hard and fast. A lot depends on fuel type and local temps, humidity etc. But I would think they should be within 1/4 turn at the most. Don't want to give anyone bad advice here, so perhaps one of our forum gurus could chip in with some expert advice on idle gap, pinch tests etc just to confirm or correct what has been posted recently :) |
Here is my test report.
I came to our local track to make test with thise setup / settings: - Go 7 Port Turbo - OS P3 plug - 0.4 mm shimmed - Jet's 25% nitro (10% oil) - long needle carb - 8.0 mm carb insert - 0.7 mm idle gap - HSN 1/2 turn in from flush - LSN 2 1/2 turns in from flush Conclusion HSN was set too rich, so I leaned it down and came to optimal settings for my engine: - HSN 1 1/4 to 1 1/2 turns in from flush LSN setting was OK (i did the pinch test), maybe 1/4 of turn less: - LSN 2 1/4 to 2 1/2 turns in from flush Engine temp never reached more than 135°C (275°F). It seems that those settings fits best for my engine. I only don't understand, why are my settings so different from other guys that own same engine. But at the end, it realy doesn't matter, because I'm very satisfied with my engine performance. |
RC Pro Series South (190 entries)
GO 3port + GO 2047 pipe 8th Place Expert Truggy (had fuel line issues which caused 2 restarts) I ran the 3R in both my buggy and truggy at this race and they were flawless. |
Originally Posted by MassiveMods
(Post 4770856)
generally you would use with a turbo head button .4 on 20% .5 for 25 % and .6 on 30%
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Originally Posted by TMizzle
(Post 4794909)
RC Pro Series South (190 entries)
GO 3port + GO 2047 pipe 8th Place Expert Truggy (had fuel line issues which caused 2 restarts) I ran the 3R in both my buggy and truggy at this race and they were flawless. Way to go TMIZZ !!!! ... (ps : - you have pending of email me back) cya !!! |
[QUOTe
It seems that those settings fits best for my engine. I only don't understand, why are my settings so different from other guys that own same engine. But at the end, it realy doesn't matter, because I'm very satisfied with my engine performance.[/QUOTE] Because that suits your set up. What is a constant is the engine but the perameters around it ie Fuel , Pipe Tyres Track < Ambinet temps etc etc are different to others , thats why your tune suits your car . Hope that helps ... MM |
while we are on an engine tuning subject i would like your opinion on this.
my engine is lacking top end power, just seams to bog at a certain speed. is my HSN too lean and my top end is starved for fuel..?? |
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