Topic: 1975 550k minimal turbo build. (Parts collected, build has begun.)

[scottly]

hi lost boy , lovely looking work ,  i have a 400/4 turbo , built in '80,

hope you don't mind me picking at something , if you angle the feed to the plenum , you will get no3 running  lean .
robert.

The angle of the feed may indeed be the cause of the current issue; the heavy fuel can't make the sharp transition to feed the left two cylinders?

[Lostboy Steve]

hi lost boy , lovely looking work ,  i have a 400/4 turbo , built in '80,

hope you don't mind me picking at something , if you angle the feed to the plenum , you will get no3 running  lean .
robert.

The angle of the feed may indeed be the cause of the current issue; the heavy fuel can't make the sharp transition to feed the left two cylinders?

Christ, I hope not. If that's the case I'll have to drill a hole in the back side of the intake and make an even longer diffuser...


Sent from my iPhone using Tapatalk

[ivanhoew]

i thought there was another unseen bit of pipe inside the plenum making the flow even ?

[Lostboy Steve]

i thought there was another unseen bit of pipe inside the plenum making the flow even ?

there is, sort of. It protrudes in and then it cut on a sharp angle to try to avoid direct pressure to hit that closest intake port. Now, however I'm wondering if I should take your advice and just weld a pipe straight on the inside of the plenum. I also have to wonder if the 170 jet is flooding the engine. It's strange, because I can't tell if it's overly rich or overly lean. I haven't run it enough to tell. I'm going to try something a bit more lean, and then if that doesn't make it any better I will introduce an even richer jet. In the minute or so that I had it running it drank that little test tank dry, that to me seems to be an absolutely insane amount of gasoline usage.


Sent from my iPhone using Tapatalk

[ivanhoew]

in case it helps LB , here's  my plenum ,made in 1980 from a bit of window frame box section .




the small dia pipe keeps the velocity up so the mixture smashes into the other side of the right angle and breaks down more ,then the box is thin wall so it warms up quickly and reduces fuel condensation .and its internal volume is enough to get an even shot to all cylinders by slowing the flow down .(its actually a little bit big for low rpm )

regards
robert

[Lostboy Steve]

That looks like I want one. last night I fiddled more and realized that it is grossly rich. It was spitting Unburned fuel out of the exhaust. The idle jet seems fine because it idles really well but pull on that throttle and it floods out. Or so it seems. The two right cylinders get warm at idle but if I rev it up they cool down and the left side gets hot.


Sent from my iPhone using Tapatalk

[Lostboy Steve]

I know someone on here knows the science behind what I'm trying to figure out as far as jetting. You're goin from 4 carbs to one larger carb. In my mind, you're still only utilizing fuel for 1 cylinder at a time however the pull from all 4 probably increases the amount of fuel being dragged out of the single carb. (Kind of the same science as to why these bikes run better with a plenum vs pods.) so maybe trying something a bit closer to stock jetting is the way to go. It does idle well on the 45 slow jet, which is just two sizes? Larger than stock. Any input on this is greatly appreciated.


Sent from my iPhone using Tapatalk

[ivanhoew]

no idea what jetting i have in my xs650 cv carb , i just drilled em  and soldered them up again and drilled etc till it ran well .that change in temp of the cylinders does suggest a mixture maldistribution . as you say ,try it on a smaller jet ,like a 140 ,and work from there .

also , that situation of running ok on tickover ,then on 2 with revving ,is a typical manifold design problem symptom .the added velocity of the incoming gases ,with rpm rising , allows the cylinder bias to become more and more pronounced .

[Lostboy Steve]

no idea what jetting i have in my xs650 cv carb , i just drilled em  and soldered them up again and drilled etc till it ran well .that change in temp of the cylinders does suggest a mixture maldistribution . as you say ,try it on a smaller jet ,like a 140 ,and work from there .

also , that situation of running ok on tickover ,then on 2 with revving ,is a typical manifold design problem symptom .the added velocity of the incoming gases ,with rpm rising , allows the cylinder bias to become more and more pronounced .

I like the solder idea. Never thought about that. I have enough jets where I can sacrifice one.


Sent from my iPhone using Tapatalk

[Lostboy Steve]

Well, Ivanhoew was correct (thank you sir). Had a coil wiring mashup which caused only 2 cylinders to fire. Fixed that. Runs pretty gd good now. Still rich as ever, I ordered some more jets to play with. I think I've answered my own question. Basically, because you only have 1 cylinder firing at a time, but combination of suction from 4 cylinders, a good base line of jetting is closer to stock than what I've been trying. So, when they arrive, A 40 idle and 105main are getting tested. As of now, even with all four cylinders getting hot, there is a mass of unburned fuel spitting out of the exhaust. Its idles high, but starts cold easily with the 60 idle jet, but you can smell (and see) how rich it is. Anyway, thats all for now.

[ivanhoew]

hurrah!

[Lostboy Steve]

hurrah!

Here's a video... With one problem solved comes another earned. I checked and it's not charging. Have to double check that wiring as well.

Sent from my iPhone using Tapatalk

[Lostboy Steve]

Made an outlet flange for my turbo. Also 3/8 mild steel.


Sent from my iPhone using Tapatalk

[Lostboy Steve]

Another video. Much better! 35/100 jetting. Still a tad rich.

Sent from my iPhone using Tapatalk

[ivanhoew]

crisp !

[Lostboy Steve]

Hey Steve (lost boy), why no updates? Ah, well because I have added yet another project to my arsenal.




Sent from my iPhone using Tapatalk

[ivanhoew]

oh good grief....focus man !