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Old 29th November 2007, 22:32   #1
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Default Improve the FE of a 4 BHP engine?

i have a small 4hp engine (honda GC135series) that i'm using for a university project.
i have to make small modifications to it so that i can improve the fuel consumption of the engine...any suggestions?

i has told to look at the carburettor as a starting point!
perhaps replace the jet for a smaller one? would this work!

i also thought maybe polishing the intake manifold!

neglible budget restricts the modifications that i can make?

any suggestions will be of great assistance
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Old 1st December 2007, 18:58   #2
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Im not sure what the final goal of this project is... but you could try the following which might make small / negligible differences :

- Change the jet
- Make sure the carb isnt leaky
- Lower the amount of oil in the engine towards the minimum suggested mark
- Clean the ports / valves / seals
- Run at optimum RPM
- Clean / choose ideal sparkplug

cya
R
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Old 1st December 2007, 19:08   #3
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From what I understand, the GC135 engines are already quite highly optimized so the gains available may be small and make your project look less than a success.
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Old 1st December 2007, 19:24   #4
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also you can increase compression and run it a little lean but you have to remember any modifications will reduce its life
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Old 3rd December 2007, 15:29   #5
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thanks!
my supervisor suggested that i look at the carb,increase compression ratio,perhaps valve timing and or spark timing. the last two modifications sound pretty complex to do?
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Old 3rd December 2007, 18:39   #6
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the last two are the easiest and can be easily reversed
try them first but they affect performance as well
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Old 4th December 2007, 23:02   #7
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if i was to increase the compression ratio...would i be looking to 'skim' the cylinder head and replace the piston with a domed piston?
any useful sites that will help me????
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Old 4th December 2007, 23:33   #8
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Default Reduce air intake resistance.

From the very limited budget that you have the easiest would be to reduce the air intake resistance by straightening the air intake plumbing and by polishing the intake piping.

The other more expensive options are to shave the cylinder head mating surface or reduce the thickness of the head gasket.

After doing the above you will have to change the valve timings and the spark ignition timings and the fuel jetting. Since fuel efficiency is upper most on your mind get the engine optimized at the pollution control center on the cheap.

Bye and wear your seat belts.
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Old 5th December 2007, 00:41   #9
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1) Increase the compression (skim the head but check for valve clearances)
2) Run the leanest mixture you can without overheating the engine (do a plug chops to determine how lean you could go)
3) Those iridium spark plugs should help to burn that lean mixture efficiently.
4) Dont go for a freer flowing filter (yes it would lean out the mixture but do it the other way round)
5) Valve timing and ignition timing are easy to do but a bit complicated. You will have to read up on it. Or do it by trial & error. Reducing the valve overlap would help theoretically in yielding a better fuel efficiency, but since your cam seems to be a one peice affair it's not that easy to do.
Retarding the valve timing is also an option, but without an adjustable cam sprocket it's hard to get the degrees right.

Are you gonna be running the engine on a bike or is it going to be a bench warmer?
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Old 11th December 2007, 01:15   #10
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Default hi

hey guys
the engine is part of a generator set.the engine may get used for other projects in the future,but just now i am looking to make the suggested mods to it to improve fuel consumption
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Old 11th December 2007, 18:07   #11
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Default No box

I do not think there is a "Petes box" for this one.

A smaller jet will also cut down the power, I think, but it seems like it should improve fuel consumption. A cleaned carb might help. Polished...maybe. Synthetic oil will give you a little gain, it is a slipperier lubricant. How about your air filter and intake? I used to just throw out the air filter and put a woman's nylon stocking over the intake for better air flow and no, I am not joking. You have to make sure it does not get sucked into the motor. Use a clamp or tie it tightly. What kind of ignition do you have? You might tinker with that.
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Old 17th January 2008, 03:48   #12
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Default ????

hi all

it appears that the GC135VHE engine that i have does not have a cylinder heas & head gasket so it is impossible to increase compression ratio!!!

would considering the valve timing make an improvement to the fuel consumption?...if so, is there any useful websites that might have a suitable camshaft for this small engine?

cheers
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Old 18th January 2008, 19:11   #13
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has the engine been hooked up to the generator ? if yes , please do the tests under load as mere idling might not give you the correct efficiency . Why dont you try playing with a 100 cc motorcycle carb ? you might have to design the constant throttle lever for use with the motorcycle lever as well .

also ,will you be running the engine on gas or with kerosene as well ?
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Old 18th January 2008, 19:32   #14
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Quote:
Originally Posted by ag501 View Post
hi all

it appears that the GC135VHE engine that i have does not have a cylinder heas & head gasket so it is impossible to increase compression ratio!!!
Oh, your engine sound like one of those with unitary cyl&head construction. But you could still increase the compression by skimming the base of the barrel.
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