Timing, Bogging, And Trying To Tune An Hif44 On A 1293

1990 Mini Racing Green (now orange, blame previous owner)

 

Engine Specs:
1293 A+

Swiftune heritage pistons

EVO001 camshaft

Big valve head

3.1 diff

standard rockers

MED ST1 lightened flywheel

LCB + RC40 DTM twin box exhaust

Alloy intake (standard from Minisport)

HIF44 w/ BDL needle, 20w SU oil in dashpot, Red spring

59D4E distributor

Gold coil (1.48v across coil, 11.68v positive coil post)

electric fuel pump

filter king regulator/filter

 

Running with 93 octane fuel (American MON) = ~98 octane (UK RON)

 

I have been told that my timing should be happy ~10-12* btdc. The issue is when I have set it this low, I encounter bogging, backfiring in mid throttle, and overall terrible throttle response for anything above idle. I've used a colortune to set the idle mixture, as well as tested the rev band with it and everything appears to look correct. I've toyed with the timing up to 15* btdc and it responds much better, to the point that I'm able to drive on the highway at wide-open-throttle and have hit ~93mph (I live in Texas, we have fast highways  ) but it still has some hesitation in 1/2-2/3 throttle. I'll break it down in detail below...

 

• 1k idle @ 12* btdc (set with vacuum disconnected and plugged)
• 1.5k @ 16* btdc (read with vacuum disconnected and plugged)
• 2k @ 20* btdc (read with vacuum disconnected and plugged)
• 3k @ 24* btdc (read with vacuum disconnected and plugged)
• Mixture is bunsun blue at idle, half/half when revving to ~2k, yellow when snapping to open throttle
• 1/4-what engine bogs down/poor throttle response, eventually backfires, cannot achieve speed greater than ~45mph

 

• 1k idle @ 15* btdc (set with vacuum disconnected and plugged)

If 15* btdc @ 1k rpm idle is considered, normal, then I'll start toying with needles.

If the common agreement is that I should be trying for 12* btdc, how?

Edited by Omnomsan, 14 October 2021 - 09:34 PM.

Unless your engine is in good standard condition the static timing is guesswork,unless your dissyhas been suitably recurved.Likewise colourtune is only useful at idle unless the needle has been reprofiled.There is no set figures,you have to give the engine what it wants,whatever that is.Welcome to non standard tuning,Steve..

The engine is fresh built and I've completed run in/first oil change just a week ago. Sounds like I'll just adjust it until it's happy and ignore the numbers :)

Try changing the dashpot oil to a drop of 20w50 (same as in the engine). I had similar bogging and found the dashpot piston was lifting too quickly and the slightly thicker oil slowed it down. The bogging disappeared.

I'm using a minispares electronic distributor (mild road, up to 276 cam) and mine is set to 14 BTDC at 1000 rpm vac disconnected. I wouldn't say there is an issue going slightly above 12? Max mechanical advance on mine is 26 degrees.

Also had an issue with it bogging/hesitating when initially pressing the throttle. After having it set up on a rolling road we found the SU oil was too thin and this caused the AFR to lean out. Switched to ATF which is slightly thicker and it fixed this issue, nice easy fix!

Just went for a short tuning drive:

raised my timing back up to 15* btdc

switched to 20w50 engine oil

 

timing helped, but no noticeable difference with the oil swap. still some hesitation in mid rev (beyond 2k) and experienced one backfire going uphill. I might need to richen the mixture even though colortune was good at idle

 

I can try swapping oil for ATF. I might also try a BBW needle and/or a yellow spring to see if those help

 

You'd think there would be plenty of dynos around Dallas with the muscle cars around, but I have yet to find one that will work with carbureted engines

You need to make the mix richer for certain stages, this is where a competent rolling road operator who knows carbs is worth the money and time

I suppose I'll need to polish my carb needle then since it runs well at idle and wide open throttle

Edited by Omnomsan, 14 October 2021 - 09:34 PM.

Just went for a short tuning drive:

raised my timing back up to 15* btdc

switched to 20w50 engine oil

 

timing helped, but no noticeable difference with the oil swap. still some hesitation in mid rev (beyond 2k) and experienced one backfire going uphill. I might need to richen the mixture even though colortune was good at idle

 

I can try swapping oil for ATF. I might also try a BBW needle and/or a yellow spring to see if those help

 

 

You'd think there would be plenty of dynos around Dallas with the muscle cars around, but I have yet to find one that will work with carbureted engines 

I'm no expert on tuning issues but that backfiring and bogging sounds like two separate problems; mixture AND timing.  Regarding mixture, I had an engine that was basically the same spec as yours and used a BDK needle with 20W Redline oil in the dashpot/red spring with good results. I also installed provisions for an AFR sensor/gauge so that I could see what the mixture was doing throughout the RPM range, otherwise, without the benefit of a rolling road and knowledgeable operator (with access to a whole array of needles) you're just chasing your tail.  I was able to try a couple of different needles to best suit how I normally drive the car and still have good throttle response.  As for timing, what is your total advance?  I'm no expert on ignition/timing but Ac Dodd on this forum is an absolute wizard when it comes modifying a distributor.  I sent my mine off to him for an advance curve modified to suit my engine.  Very satisfied with the result.  I found that once you stray from a stock engine you have to fiddle with tuning to get the best result for the new configuration-the figures given in the Haynes manual are just a good starting point. 

Edited by croc7, 14 October 2021 - 09:17 PM.

Just get a basic power run on the Dyno if they not interested in tuning. You don't need them to be willing to tweak the carb so long as they're happy to do an afr trace on your power run. This will tell you a lot and where it is lean and you'll be able to get an appropriate needle using the various needle charts (mintylamb is good), or you could polish your own. You'll be looking at richening the mixture at about 1/4-1/3 of the way down from the top hat of the needle if you're struggling with cruise and partial throttle.

I solved the timing issue finally, but at an expense. The vernier cam gear bolts came loose so my static timing was bouncing around which prevented me getting an accurate read. That's been fixed now and it happily runs at 12° BTDC.

After getting that fixed...
[AFR Test 1 with MTX-L Plus]
• HIF44 w/ BBW needle & yellow spring
• Timing @ 12° BTDC
• Engine Temp ~70-80C (ambient 10C)
• Gauge/sensor calibrated in open air per instructions

• Idle: 10.5
• Accelerating: 14-16
• Low speed cruising ~65kmh: 13.8-14.2
• (Texas) Highway cruising ~130kmh/4.5krpm: 14.5
• Wide open throttle: ~13
• Top speed: 150kmh

Expecting a leaner idle, I fiddled with the mixture to lean out my idle, got it up to 12-13 AFR but then it wouldn't idle lower than 12-13krpm. Adjusting the idle screw had no effect. I retarder the timing advance to get the idle back down but then it just bogged when revving. So then I adjusted the mixture back to ~11AFR and the idle settled back down to ~1.2krpm. That idle is too high, so I set everything back to where it was for now. I guess I'll just live with a richer idle. I've encountered this issue before but never did solve it on the 998.

Sounds like you need another, possibly a custom needle

Just wanted to follow up on this thread and mark it as solved. Your advice got me sorted and it was the fast idle that was the culprit. I've been driving it happily since :)

If you ever want to put it on a rolling road with guys who know what they're doing with LBC's, take it up to Jesse Prather Racing in Topeka - he'll get it sorted. If you ever decide to come up let me know and I'll meet you there, I have a small assortment of HIF 44 needles.

Edited by Magneto, 08 May 2022 - 12:00 AM.