Landracing Forum

Tech Information => EFI Questions => Topic started by: generatorshovel on August 31, 2012, 07:58:40 PM

Title: Draw thru supercharger carb weirdness
Post by: generatorshovel on August 31, 2012, 07:58:40 PM
I'm having trouble setting the carb jetting, (250cc/4, aisin AMR300 / alcohol)
Carb #1 HSR42 Mikuni, alcohol supplied from a reputable supplier whom I've dealt with previously.
Filthy rich, fuel spraying from exhaust while warming up.
Ive re-jetted the pilot jet which cured the fuel spitting, the bike answered to gobs of throttle in the shed ok, but a test ride showed a problem with engine cutout over 1/4 throttle.
Needle jet and needle changed, problem persisted
Main jet changed from way too rich, to a tad lean,,with no noticeable change in the engine cutout problem.
In an attempt to eliminate the carb from the equation, I fitted the smaller carb from my LSR 175cc single (Iv'e calculated the 42mm flows 190 CFM, and the engine,with 10 psi boost, would require 110 CFM, the 32mm carb is close to this number)
Straight away, with the smaller carb (which an fine on the other engine) the ugly fuel spray from the exhaust @ a 3,000 rpm idle problem returned, and the engine drowns before warming up is achieved.
Why ?
What effect does a supercharger have upon a carb that will make it run so rich at idle, when it's jetted "right" for a non blown engine
I can reduce the jetting, but other than the idle mixture screw (air) this involves a smaller pilot jet, which is fine for small throttle openings, but the transition from pilot, to needle jet seems to be where the problem is ?
I've tried rolling the throttle past the cutout point, to see if the main jet can pick up the slack,,but the engine doesn't recover untill the throttle is returned to under 1/4 throttle.
I have plenty of fuel flow (pump) about 2 ltr/min
(http://i1195.photobucket.com/albums/aa399/Blowncbr/10-11-2.jpg)

https://www.youtube.com/watch?v=TVr_gdo52so

Tiny
Title: Re: Draw thru supercharger carb weirdness
Post by: Milwaukee Midget on August 31, 2012, 08:31:54 PM
Limited to my experience with a supercharged MGB, but -

First thought always turns to ignition.  If it's spitting fuel out the exhaust, something is not burning.  Weak spark/too much spark gap is the first thing I'd check.  According to electromotive, a little less gap when pressure goes up is advisable.

You mentioned good flow - but too much pressure, perhaps?

Title: Re: Draw thru supercharger carb weirdness
Post by: generatorshovel on August 31, 2012, 09:07:46 PM
First thought always turns to ignition.  If it's spitting fuel out the exhaust, something is not burning.  Weak spark/too much spark gap is the first thing I'd check.  According to electromotive, a little less gap when pressure goes up is advisable.

You mentioned good flow - but too much pressure, perhaps?


Thanks chris ?
I'm aware of the potential ign energy problem (have a fist full or iridiums gapped @ .020" ready) and found a place in the UK who do a mean coil to suit the lil hondas
The pump is regulated to 4psi, with a suitable needle/seat fitted.
Maybe I'll have to live with the spitting of unburnt fuel problem, just to hav e it rideable at full noise ?
Maybe the fuel is falling out of suspension when it gets to the rather large, cold plenum (I forget what capacity I worked out the intake volume was,but did the research before fab)
I haven't spoken  with Doc G since his return, I hope your blokes didn't abuse his tired 'ol body too much during his visit?
Tiny
Title: Re: Draw thru supercharger carb weirdness
Post by: Bob Drury on August 31, 2012, 11:00:22 PM
  Shovel, the fastest pass so far in my 496 BBC on straight methanol it left the line spewing raw fuel out the exhaust (according to my engine builder) and it was so fat that the plugs had absolutley no sign of use, all the cad was still on not only the threads but still on the ground straps.
  If I had not pulled the plugs myself, I would not have believed it.
  What I am saying is don't freak out unless it won't clean out under power or just plain feels like it has nosed over.
  One thing to remember with alcohol (or any other non petroleum based fuel such as Nitro, is that when the motor is cold or idling, the fuel is running right past the rings and diluting the oil (and filling the crank case).
  I try to preheat the oil and water and start it, clean it out, and go like hell.        Bob
  One more thought, if the blower has tight clearances (roots type) maybee it is pulling a vacuum above the rotors and actually literaly pulling fuel through the carb.
  Perhaps you are running too much fuel pressure to the carb.
  I really have no idea what I am talking about cause its a Blue Moon here on the top of the World...........................
  p.s. Don't forget to run a alcohol lube such as Red Line as the methanol will wash the oil off of the cylinder walls which is not a good thing at all.
Title: Re: Draw thru supercharger carb weirdness
Post by: Milwaukee Midget on August 31, 2012, 11:32:49 PM
No abuse of the Doctor on my part - I was only in contact via phone - stuck in Beerhaven, again.

One other thought - did you just convert this over to alcohol?  Are there floats?  Alcohol is heavier than petrol, and I'm wondering if that might be causing the floats to keep the bowl jet open and flood it out.

I'm running about 2.5-3 psi on my SU and on my Weber to avoid overfilling the bowl.

I'm taking stabs in the dark, but I am very interested in the solution you come up with.

Chris
Title: Re: Draw thru supercharger carb weirdness
Post by: Dr Goggles on August 31, 2012, 11:37:35 PM
If it's spitting fuel out the exhaust, something is not burning.  Weak spark/too
I haven't spoken  with Doc G since his return, I hope your blokes didn't abuse his tired 'ol body too much during his visit?
Tiny

Just ran a diagnostic, got a pulse here, O2 sensor reading normal zone. Thanks to Carmen's I was spitting a bit of unburnt alcohol out the exhaust early in the week at Wind-Over, Having proper work to do in LA kept my nose clean.....as did the impending start to my new job three days after disembarkation at Tullamarine....I'm positively healthy right now, off for a creek-walk/bird-watch this arv'.
Title: Re: Draw thru supercharger carb weirdness
Post by: hotrod on August 31, 2012, 11:39:40 PM
You might want to put a vacuum gauge on the intake below the carburetor to see how much vacuum signal the carb is seeing. They are only designed to work within the typical vacuum range seen in a NA engine. I as mentioned above the blower is pulling a vacuum in the intake, it could be sucking fuel right past the butterfly, transfer slots etc.

Larry
Title: Re: Draw thru supercharger carb weirdness
Post by: generatorshovel on September 01, 2012, 12:52:29 AM
Thanks Guys (blokes)
Bob & Larry,I think your on the money with the carb/blower vacuum , The thought has entered my mind  :? What to to to solve it, I dunno, yet.
The engine has done about 1 hour, 3 miles, and 3 oil changes, I'm also onto the oil pollution thing. )I'm a tad worried about hydrailic lock at the moment.

Chris,
I bench tested the carb / pump / regulator combo @ 4PSI with no sign of overflowing.
The carb(s) were set up by "pure power" (Jim Payne) for use on Jr Dragsters
Have I mentioned its a pain in the freckle to start (cold) when its set up as it is now ? (Aerostart needed)

Doc,
     I'm pleased to read you left a good collection of your grey matter in Bendover mate,
You still crack me up when I need a smile fix.
Tiny
EDIT
I finally got some heat into it, and monitored the dribbles, bugg'rall smell , and settles once the heat gets in, there's a fair amount of condensation going on in the collector I think (ambient temp 65 degrees here)
I had time to play with the idle mixture screw this time (on 'tuther side from throttle) starting with 1 1/2 turns out, poor throttle response, then 2 turns,,same result,,then 2 3/4 out,,it stopped.
Restarted with 3/4 out, it started to hunt (It's always done that) and throttle response improved, so I went with 1/4 turn,,,vast improvement,,but still sounds lean just above idle, but manages to hurt my ears when blipped from past that.
That "fuel" might be mostly water ? although it made Mrs "T" gag when I poked a wet finger in her nose, for a second opinion  :evil:
I'm gonna up the pilot jet and try again.
EDIT # 2
Manifold vacuum is 18" @ idle, raising to 20" just above idle.The fuel dribbles have stopped ?
#65 pilot jet is in, it seems close enough for another test ride, get some uniform heat into it, and play with needle position and main jet if needed.
Title: Re: Draw thru supercharger carb weirdness
Post by: Moxnix on September 01, 2012, 03:22:45 AM
A float bowl spacerfor the HSR42 is available from Mr. Turbo in Houston, a bit spendy, maybe you can make one.
Title: Re: Draw thru supercharger carb weirdness
Post by: generatorshovel on September 01, 2012, 04:38:22 AM
A float bowl spacerfor the HSR42 is available from Mr. Turbo in Houston, a bit spendy, maybe you can make one.
Thanks Moxnix, Iv'e looked @ those, but if another few ounces of fuel won't make much difference, if the supply & demand ain't right.
Plus,,its awkward enough to swap main jets already, without not being able to see 'em too.
Hey,,,how's your voice after Bubs ?
Tiny
Title: Re: Draw thru supercharger carb weirdness
Post by: Queeziryder on September 01, 2012, 07:47:21 AM
Tiny

Something that may help with warm-up is to get yoiurself a sure-shot spary can, fill it with gas, pressurise and spray gas down the carb throat with the methanol turned off. (old top fuel bike trick)
This will reduce ring wash whilst warming the engine, and probably make tuning the engine easier.

HTH
Neil
Title: Re: Draw thru supercharger carb weirdness
Post by: Moxnix on September 01, 2012, 09:23:58 AM
Oh, my delusional self-importance made me post that.  I have a face for radio and a voice for print.

If you were running 20 lbs. of boost, it might be a valid suggestion.

My voice never came across the webwaves, I kept running notes over to the radio tent for the 4 announcers to share.  Delvene, Denis Manning's daughter, runs the meet; she is an Ozzie, smiled when I told her someone in Broken Hill, NSW was tuning in.
Title: Re: Draw thru supercharger carb weirdness
Post by: SPARKY on September 01, 2012, 12:59:41 PM
What I use is a Propane bottle with a regulator and about 8' yes feet of copper line with one-way flashback protectors ---from oxy-acclene--in the line.  put the line over the intake opening--- much safer and much more controlable when one shuts off the gas there is virtually no danger from lingering fuel.
Title: Re: Draw thru supercharger carb weirdness
Post by: kiwi belly tank on September 01, 2012, 03:30:19 PM
Sounds to me like you are probably fighting low speed rotor pulse here mate. Its especially a problem with two segment rotors & the closer the carb is to the blower, the worse it gets. The carb is responding to a huge signal & then nothing & the engine's on the receiving end going WTF.
This is why SU's work so well in this type of situation, they have a variable main plus they are a variable air flow carb so too big or too small never happens.
You might want to check & see if you are having a problem with manifold icing during warm up too.
Once you get into hot run mode, keep checking all the plugs to make sure you're not having a distribution issue.
  Sid.
Title: Re: Draw thru supercharger carb weirdness
Post by: Dean Los Angeles on September 01, 2012, 05:20:41 PM
One other thought is vibration might be causing the cutout at high speed. Clamp some lead around the intake bell. Solder works.
Title: Re: Draw thru supercharger carb weirdness
Post by: generatorshovel on September 01, 2012, 07:55:08 PM
Once again, thanks to all for your valued input  :cheers:
There is no substitute for experience, and this forum has experience dripping from it's ears,
One of the best things I have gained from this build, is learning new skills, even if they were obtained the hard way sometimes, I'm an old dog, and have learned new tricks, hopefully I will be able to share some info and help someone my self one day ?
Tiny
Title: Re: Draw thru supercharger carb weirdness
Post by: generatorshovel on September 09, 2012, 02:55:53 AM
The process of elimination took a giant leap forward today  :-D
The ignition output is satisfactory, .036" plug gap, full throttle, 14000 rpm in 5th, no problem  :-D  (although it began to nose over  after a while in 5th gear indicating fuel flow problems)
1 more gear, and 1000 rpm to go !
 :cheers: Tiny
Title: Re: Draw thru supercharger carb weirdness
Post by: guilfordin on February 16, 2015, 12:18:58 PM
I think I read you are running a 250cc Suzuki 4 cylinder/water cooled engine?  I just picked up a bike here in Indiana, USA for use at the Bonneville Salt Flats.  I have a 500 cc Suzuki two cylinder air cooled bike that I ran in 2012.  I was considering a supercharged application for the little 250 but don't know if the AMR300 is a good choice.  All those 125, 250 350 and 500 cc land speed records are held by two stroke Yamaha's, so the only way to counter that is with boosted 4 strokes.  I have had good experiences with turbocharging, and may just go ahead and build one for this class.  To make serious power, is going to require at least 20 PSI, not sure if these little things can do that.  I see no problem turning the 250 at 18,000 + RPM with performance valve gear.  I use hastaloy exhaust and titanium intakes, with stiffer springs and titanium retainers. 

My fuel/air ratio is 4.6"1.  With alcohol, its very hard to figure how much to dump in.  (http://[img])[/img]
Title: Re: Draw thru supercharger carb weirdness
Post by: generatorshovel on February 16, 2015, 10:10:42 PM
Close Guilfordin, I'm running a Honda 250/4, and have sorted out all my fuel issues now.
These Hondas are happy until an indicated 18,000 rpm (it's actually 17,200), then the valves tend to bounce (surprise !  :roll:)although power peaks @ 15,200 (actual) , anything more is just for young bloke bragging rights,,,,,I have a spare engine (parts only) that had dropped a valve, all pistons had polished valve pockets from valves bouncing off 'em, Honda got the cutouts right, the valves hit square onto the piston cutouts.
http://youtu.be/oNbWwK05phQ
The exh valves are Titanium standard, or more correctly, the tulips are, the stems aren't and they also contain a fair bit of unobtanium ( a set on evil bay UK at the moment for 50 quid each !)
Engine consumables are also rare, Honda NEVER made 0/S pistons, big end shells are impossible to buy (so far), as are mains.
When I rebuilt my engine, I used CB250F cams (zero overlap, .5 mm less lift), which upped the pre-determined boost from 9 psi, to 15, with no blower drive changes, the bike has done very little testing @ 15 psi, I re-geared the blower to drop back down to 10 lb, once I actually get a slip,,I might go for broke with 15 ?
Red cup racing from Canada have a turbo'd 250/4 they are sorting out now, plus a de-sleeved 250/4, which is now a 175/4  :-o
I with them well with their racing year.
Hopefully, I'll get some salt in my veins soon  :cheers:
Title: Re: Draw thru supercharger carb weirdness
Post by: guilfordin on February 16, 2015, 10:29:13 PM
When I decided to try the 250 Class, I went on Craigslist with a want ad for any four stroke 4 banger, Yamaha, Suzuki or Honda.  As you may not know, these were never sold for sale in the US.  I've never ridden any of them, I just based my quest for something that could handle the TZ's out there.  It would be nice if the sanctioning bodies broke out two stroke and four, but I think that 110-120 BHP is easily attainable with pressure and fuel.  Here is a link to a dyno run three years ago

https://www.youtube.com/watch?v=YzzpNypsviA

, running straight methanol, 20% throttle setting, and 11,000 RPM rev limiter.  We crashed 200 several times afterwards, but I was plagued with breakage, which turned out to be from hydro locking.  Turns out the rev limiter was killing spark, but not fuel, and was twisting rods off at the pin.

On this 250, I really want to run one of those AMR300 units, but not as a draw through.  EFI is still the way to go, but there is a huge tuning curve to deal with if you start running anything other that E85 or race gas.  Regarding pistons, I have been using Ross forever, absolutely a great choice and they can make anything.  I liked reading about the desleeved 250, I was going to sleeve down one of my 400 bandits, but I wouldn't be able to get enough compression to run alcohol.  I couldn't find any crank builders who could destroke it either.  Those boys from IOM in England did that with the 600 Yamaha, and killed the 500CC record last year.
Adding a pic of what real detonation looks like ! Yikes, getting sick of this.
Title: Re: Draw thru supercharger carb weirdness
Post by: generatorshovel on February 16, 2015, 10:32:52 PM
Thanks for assisting my post night shift wake up struggle ,,read this,,,
http://cbr250.com/forums/project-bikes/7307-project-cbr250rri.html