Technical Why could my 594cc engine be underperforming?

[smart51]

Mathematically both the 115/190/50 and 125/205/50 are same ratios to main to air (+-60%) but with larger size of Jets.

Kind of. I found the 115 combination was too lean at low air flow and 125 was too rich at the top end and changing the air jet only altered that slightly. I found a 120 main enriched the low end enough, without making the top end too rich.

 

[the hobbler]

Thank you ‘The Hobbler’ I tryed 120 main jet with 190 Air Jet 50 Idle jet. It definitely improved the power versus 115 Main Jet 190 Air Jet and 50 Idle. I am know experimenting with 125 Main 215 Air 50 Idle this feels almost the same as 115/190/50 combination. My next experiment will be 125 Main Jet, 205 Air Jet and 50 idle Jet. Mathematically both the 115/190/50 and 125/205/50 are same ratios to main to air (+-60%) but with larger size of Jets. Let’s see if staying with factory ratios for 652 engine, this time with larger jets would make a difference.

Looking at your comments, it would seem that you ARE keeping a careful log of ALL jets changes---what too and when. Doing this is very important (essentle in fact), because if you don't it is very easy to forget WHAT you have in the carb, and when you did it.

 

[Domkat]

Kind of. I found the 115 combination was too lean at low air flow and 125 was too rich at the top end and changing the air jet only altered that slightly. I found a 120 main enriched the low end enough, without making the top end too rich.

652 cc engine with Weber 28 IMB 115/190/50 definitely producing most predictable performance, 120/190/50 definitely had more low end power but not added much to top speed. It Aldo came at the expense of 10% higher fuel consumption (Not that it matters but for the records). Current 125/215/50 is an improvement over 115/190/50, will soon find out how it is when it comes to fuel usage. My next experiment will be 125/205/50. I am hoping some where in between all this combinations I will be able to get optimal performance out of my engine.

Looking at your comments, it would seem that you ARE keeping a careful log of ALL jets changes---what too and when. Doing this is very important (essentle in fact), because if you don't it is very easy to forget WHAT you have in the carb, and when you did it.

By the time I finish, I will be proud owner of entire series of Weber main & air jets. I will keep you updated on the performance of each combo.

 

[Domkat]

I finally finished my experimentation with Weber 28 IMB carburetor.
My 500 has an 650 cc 35 HP engine, a sport camshaft 40/80, enlarged valves 35.3 mm/28 mm and a sport timing chain kit. I experimented with every possible Main Jet, Air Jet and Idle Jet combination.
I drove the Car under each combination consuming full tank of gas and after each test put it on Dyno test.
Best performance was 125 Main Jet 215 Air Jet 45 Idle Jet. This combination made it ideal for high RPM performance and aggressive driving. Reaching 73 miles top speed. Leaning out the mixture at high RPMs (35 miles per US Gallon fuel consumption).
Second best combination was 125 Main Jet, 205 Air Jet 50 Idle Jet combination gave Slightly richer low to mid-range performance, however higher fuel consumption (31.5 miles per US Gallon).
Third combination 115 Main Jet, 190 Air Jet, 50 Idle Jet made gave smooth throttle response and balanced fuel delivery making it more suitable for daily driving or relaxed cruising.

 

[smart51]

That makes sense. A 115 main with a 190 air jet is roughly comparable to a 120 main with a 205 air jet, half way between your preferred setting. 35 MPG (US) is equivalent to 42 MPG (Imperial). I get 42.5 from mine.

 

[Domkat]

That makes sense. A 115 main with a 190 air jet is roughly comparable to a 120 main with a 205 air jet, half way between your preferred setting. 35 MPG (US) is equivalent to 42 MPG (Imperial). I get 42.5 from mine.

BTW. I also tried a 120 Main Jet 190 Air Jet 50 Idle Jet combination, whilst it had good low and high end performance it was running too rich gave much higher fuel consumption of 29.5 miles per US Gallon.