bricheun
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| posted on 3/11/06 at 12:44 PM |
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Low RPM full thottle stumble
Engine : 1600 D16A6 Honda
Camshaft - Delta 272
Fuelling - Keihin Dual carbs 35mm
Cam timing -1 degrees
Ignition -8degrees
I have this problem with the fuelling(?) or something else but there is stumble and hestitation when I put full throttle from idle. It gains RPM
slowly hestitating from 800rpm to 1500rpm, then it becomes normal again. The engine is like saying " hold on...brrrrrr.." then "oh
lets go.."
Mid range from 2000 to 6000 is nice and strong and can take full throttle. I have raised the needle 1 mm only to make the mid range slightly better
and top end very soft, struggles to 7000. No difference in the stumbling situation.
The problem gets worse when the engine is hot.
Idle A/F is around 13-14.
High RPM around 12.
Is the stumbling caused by being too rich or too lean?
Should I lower the fuel level in the bowls?
ANy advice is welcome..thanks.
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bricheun
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| posted on 3/11/06 at 12:45 PM |
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Oh I forgot to add, if I gradually press the throttle, there is no stumbling, once I increased the rpm to 1500 then full throttle also shows no
problems.
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nib1980
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| posted on 3/11/06 at 12:49 PM |
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sounds a little like fuel starvation at low end. what fuel pump are you using?
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bricheun
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| posted on 3/11/06 at 01:17 PM |
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It is a mechanical fuel pump, it is attached to the camshaft and pumps away.
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Danozeman
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| posted on 3/11/06 at 01:18 PM |
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I have a similar problem on my zetec and cannot solve it..
Dan
Built the purple peril!! Let the modifications begin!!
http://www.eastangliankitcars.co.uk
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02GF74
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| posted on 3/11/06 at 01:31 PM |
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is there some enrichment mechanism, like on webe/dellorto?
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NS Dev
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| posted on 3/11/06 at 01:48 PM |
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800 to 1500 on a 1600 engine, with most engines this will make them falter!!
You can make accel fuel delivery greater to cover it but it will prob make it fluffier on sharp throttle opening further up the rev range.
Just don't floor it from idle!!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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bricheun
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| posted on 3/11/06 at 02:29 PM |
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So this problem is going to stay with us all who has this problem. I suppose it could be the inertia of the flywheel and other stuff.
I was expecting them to rev up quickly as in the bike engines :-)
I will return the setting to standard to lean of the mid and high end. It seems more sluggish rich and does not want to rev up as freely. Leaner is
supposed to give more power.
Strange thing is the spark plug ceramic is white with a little brown speckles. The hook electrode is clean , grey/black color and the round base metal
part is black.
Assuming you read the ceramic part it is lean, but the base round metal part is black/sooty.
Is this lean or rich?
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bricheun
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| posted on 3/11/06 at 03:41 PM |
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http://cochise.uia.net/pkelley2/sparkplugreading.html
This is the proper way to read a plug..I read it wrong, it is not observing the porcelain, it is the base ring.
My base ring was black with some sooty deposits before I adjusted it to be richer.
Hence it is now even richer which explains why is lower on power at the top end of the rpm.
I will adjust it back down tomorrrow and lower the float level 1 mm or so and see the changes.
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MkIndy7
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| posted on 3/11/06 at 06:42 PM |
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Have you tried changing the timeing or where it advances or retards?
Our Webber Twin 40's were like that till we Changed the timeing on the Megajolt,
It might just need retarding slightly in there range where you want sudden acceleration.
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DIY Si
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| posted on 3/11/06 at 06:54 PM |
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I think it's just because of the rev range. No engine is exactly lively at such low revs. It'd be a bit like pulling away at tick over,
fine if you want to go slowly, but at speed? Forget it! Either build the revs higher, or go down a gear or two. Or even three from 800 rpm. Possibly
even get away with 4 gears! 
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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JoelP
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| posted on 3/11/06 at 07:19 PM |
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ive had the same, someone described it to me as the engine being unable to cope with the sudden rush of fuel and air at such low speeds.
and yeah, the solution was to open the throttle more gently. 
[Edited on 3/11/06 by JoelP]
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mark chandler
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| posted on 3/11/06 at 07:30 PM |
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If your carbs have got butterflies to open the venturi & dampers that sit behind the jets ala most bike carbs then you need to slow the damper.
In the old days with SU's (which is what you effectively have) you changed springs and thickness of oil so that the damper rises with engine
revs.
When you floor it the damper lags slightly causing a rich mixture.
Most people replacing SU's with webbers etc feel a kick in the back when floored, not so with correctly set up SU's, the kick is infact a
flat spot prior to power coming on withe webers and indicates a poor set up.
I suggest you have a looksee at the carbs and see if you have any control over the damper. If the springs etc are all set then you could try reducing
the size of the air hole that allows the vacumn to build.
Regards Mark
[Edited on 3/11/06 by mark chandler]
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bricheun
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| posted on 4/11/06 at 03:39 AM |
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The keihins I have do not have a damper setting on the slides, it is just a spring and 3 small holes at the bottom, goes up and down pretty quick.
I did reverse what I did but leaning it out a little and it did get better. I reduced the amount of fuel squirted in for the accelerator pump and
lowered the fuel float by 1.5mm and it has improved the situation.
Now off to test it on the open road...
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millenniumtree
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| posted on 4/11/06 at 04:38 AM |
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I have a D15B1 in my old civic. It's injected, but it does about the same thing if you accelerate from low revs up through the higher range.
Starts out VERY sluggish, then once it reaches its happy point, it'll throw you back in your seat.
I did have a very nice performance boost by just replacing the air filter. You're probably way past that, but just in case you forgot about the
basics like I did for over a year... 
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bricheun
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| posted on 4/11/06 at 05:39 AM |
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hahaha..yeah I checked that. I have a K&N filter on it.
Strange - lowering the fuel level make the mixture richer - wow--A/F 10 -12 through out the rev range, something is wrong. But it don;t half pull now
;-)
Gonna get it check out now.
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