Technical Low rpm on rebuilt gx160

[mreed707]

Hi,

I am not experienced at all in rebuilding engines or knowing much about engines but have given it a go to learn.

Carefully sourced parts and 100% sure parts correct as per engine type etc

Cleaned engine as carbon deposits heavy in cylinder head. Cleaned carb. I replaced piston and rings, replaced valve and springs (gx140)Honed cylinder and lapped valves, ran in through stages of increased rpm on track using alfanso rev counter.

When sat on kart trolley and blipping, see up to and over 5000 rpm. When on track see max 3800 and does not increase.

Set valves to .004 intake and .008 exhaust. Not Honda spec but this was advised on uk karting website.

Engine back fires after blipping did not do this before. When replaced oil after run in was really dark black. Not sure if this is exhaust or what happens when running in an engine.

I have since checked the carb and is clean as a whistle.

Spark plug is clean and has been tightly fitted not loose.

So it seems on start up rev range can be achieved but under load on track, does not.

I’m going to strip again and look at the following

Check piston rings as might be a compression issue(?)
Set valves to Honda spec
Check ignition coil gap

I don’t know why I’m having the issue so unsure of how best to approach the problem.

Has anybody had a similar issue or any advice on what to consider.

Cheers

 

[mreed707]

I’ve also since discovered oil in the vacuum pulse feed. Does the pump need to be cleaned or replaced? Could this be the cause of my issues?

 

[LE#99]

Carefully sourced parts and 100% sure parts correct as per engine type etc

Cleaned engine as carbon deposits heavy in cylinder head. Cleaned carb. I replaced piston and rings, replaced valve and springs (gx140)Honed cylinder and lapped valves, ran in through stages of increased rpm on track using alfanso rev counter.

Should not clean the carbon, this is one of the things that give the engine more power.

When sat on kart trolley and blipping, see up to and over 5000 rpm. When on track see max 3800 and does not increase.

Should be getting 6500 on track or up to that depending

Set valves to .004 intake and .008 exhaust. Not Honda spec but this was advised on uk karting website.

Engine back fires after blipping did not do this before. When replaced oil after run in was really dark black. Not sure if this is exhaust or what happens when running in an engine.

The backfiring is normal

I have since checked the carb and is clean as a whistle.

Have you made sure all the jets and emulsion tubes are clean?

Spark plug is clean and has been tightly fitted not loose.

So it seems on start up rev range can be achieved but under load on track, does not.

What gearing are you using on which track etc

I’m going to strip again and look at the following

Check piston rings as might be a compression issue(?)
Set valves to Honda spec
Check ignition coil gap

Have you set the ignition to the msa regs?

I don’t know why I’m having the issue so unsure of how best to approach the problem.

Has anybody had a similar issue or any advice on what to consider.

Cheers

Check to see if there are any leaks I guess.

Not much help but hope it at least helps a little

 

[mandelbug]

How are you measuring the revs? I always found on our 160 that the reliable way was plugged in to the On/Off switch rather than wrapped around the HT lead. On the HT lead we would see very erratic readings on track, quite often below 4k when we knew he was flat and doing more