52 replies to this topic

[mailman]

Does the needle position relate to the position of the throttle, or to the engine speed?

[jaydee]

Relates to the vacuum of the engine, which is dependant on the load you put on the engine.

Best way to tell the position of the needle under certain conditions, is to put a graduated stick in the dashpot in place of the damper.

[mailman]

Ok, I've spent the afternoon mucking around with the mini. I tried a yellow spring, that seemed to help initially but meant that it was running quite lean at cruise. I removed the carb and stripped it down to make sure that the everything was working as it should. It all appeared to be in good nick.

 

I am now debating whether I need to try a new needle with the new (yellow) spring, or go back to the lighter (red) spring.

 

Thanks Jaydee! I am just unsure about doing that method since I need to be out driving around to have the engine under any load. I could do that in the garage I suppose but revving to 5000rpm (where my biggest issues are) in neutral isn't pleasant, and doesn't sit well with my mechanical sympathy.

 

if I am trying to get extra fuel in to prevent the excessive lean conditions at 5000rpm and up, does that use the same part of the needle as going full throttle lower in the rev range?

[jaydee]

I doubt that at 5000 rpm in neutral you'll get any higher than station 4

[mailman]

That's my point, do you know whether the stages are more related to revs or throttle position?

I'm having issues getting enough fuel at high revs. It's quite confusing. And hard to keep track of everything when having to stop, change needle, jet height, or whatever, and then get back out. I need to get my own AFR measuring set up so I can take things a bit slower.

[jaydee]

It relates to both in some manner, its hard to guess without putting hands on the engine. Id really reccomend using the stick to see what going on in the carb. You'll soon work out yourself.

Much easier to have it tuned on a rolling road, saves the hassle of filing down a pile of needles before getting it right..

 

What i can say is, start with a confortable idle, 3.5 CO at 1000 rpm which is 13.2 AFR but at idle it will jump up and down by a minimum .5 up to 2-3 depending on the ignition, thats why its better to set it with a gas tester.

 

Then once it sits comfy at 3.5 CO idling with engine warm, you can start tuning cruising stations.

I dont remember exactly the positions with the HIF44, but i kinda recall that in top gear it was something like station 2 = 2000 rpm station 3 = 3000. I used a stick in the dashpot to measure exactly where it sits at 2000 rpm, 2500 rpm, 3000 rpm etc so i'd reccomend doing the same thing.

You dont have a dyno, just go to a closed area, get a stick, make a graduated scale possibly in different colours (makes it easy to see!) and drive around with no bonnet and the stick in place of carb damper. It works. See what your AFR gauge is telling for cruising at 2000 in 3rd gear first.

File down with 600 grit a very small amount at time at the given point if its too lean, and a even smaller amount on the further down stations.

Move up in the cruising range in 500 rpm increments i avoid to to the cruisings above 4500 rpm, these will cross to the transition to full throttle.

Once you've done the cruising, you check with your AFR meter full throttle runs in 3rd gear from say, 2500-3000 rpm.

As you puch the throttle if the meter is suddenly showing 10 or less AFR although it might look effective for a torquey pick-up, it will not the best to achieve full power, carb will be 'stalling' at a certain point. Thinner oil in the dashpot can help under this aspect.

Under full throttle, if you can get a steady 11.3 AFR as the engine is going up through the revs, then its good. a floating of 0.5-1.0 in the afr is not too much trouble, but you can do further testing.

When it first pick up as you floor the throttle, dashpot wont actually rise up from its cruising station, then goes straight to the stations that are between 6 and 9. Then it will slowly get higher up to station 13. The time it takes to get moving is mainly governed by carb damper.

 

Hope this helps.

Edited by jaydee, 12 September 2013 - 11:04 AM.

[mailman]

Thanks. Definitely helps!

I think I may have to try making the stick. 5/16 dowelor something else?

[jaydee]

Been using chinese sticks for years