Topic: 592cc Engine Jetting Issues

[turboguzzi]

Dyna s can give all sorts of headaches, even when seemingly sparking well . i just dont trust that system. would even fit points for a while just to make sure thats not the problem

are you running resistor plugs and caps? if not, please do. ... that's another source for all kind of misfires...

[TwoTired]

Be aware, I am just trying to help you, not just run you around in circles.  But, the endeavor is difficult without any hard data to analyze.

Latest - rejetted carbs to a #100 main jet (stock is 98),

Probably still too small a main.  The #98 was selected because of the stock high pressure muffler.  All the 4 into 4 used a #100 main.
I really think you need a WOT plug chop to zero in on the correct main jet size.  Multi throttle position ride arounds aren't going to get you the proper information to make a predictive change, imo.

Am I correct that you have changed the venturi shape on these carbs?  If so, that is a serious change in pressure drop when the air velocity increases. Probably much less than before, which would seriously change the flow rate of any fuel jet installed.  Further, if the shape is no longer round, then I suspect there is also atomization issues, too.

left slow jet at #38 (stock) and needle at 2nd clip down from top (stock).

This needle position only applied to the stock CB550F engine/muffler with the paper air filter.
The K models with the exact same engine, filter,  and only the 4 to 4 exhaust system change, had the needle in 4th position from the top.   So, the question is, do you think your current set up is more like the 4 into 4 tuning or the F model high pressure single muffler?

Retained the Unipod filters and set air screws at 1.5 turns (stock). It still burbles and hesitates at low throttle openings and immediately off idle.

I'm thinking your description of burble is different from mine.
Anyway the 77 Cb550 F had the stock pilot screw sett as 1 1/4 turns.  However, with the shortened intake tract and pods that is almost certainly to lean for an acceptable throttle response off idle.  It's going to be less 3/4 to 1 turn max, when using the #38 pilot.  The pods may even demand a #40 pilot jet.

I'll make this point again.  I simply don't believe you can compare the PD carb jetting to the early style carbs (022a,069a, etc.)  It is very easy to see the venturi shape has changed between those carbs.  And, I suspect that one of the improvements associated with those PD carbs is improved atomization, as Honda and Keihin were working toward the EPA 1978 mandates.
Notice there is no 1978 CB550F?  The product line for the F ended in 1977.  Only the 78 CB550K with the PD carbs made the grade.

If the venturi shape has indeed been altered, who knows how well these carbs can work at any but WOT.

My advise is to find some PD50 carbs from a CB650.  You can run the engine lean at idle and the accelerator pumps makes throttle twist a joy.  You'll still have to tweak jetting for best mixtures, as no engine has the same demands as what you have configured now.

Cheers,

[Flying J]

Here is a crazy question for you Lloyd. Do you think its possible to fit a set of 550 pd carbs with an accl. pump from a 750. I have almost all the parts. Would just need to remove them and drill the holes in the 550 carbs.

MAde a post so i dont hijack
http://forums.sohc4.net/index.php?topic=107703.new#new

[Kemp]

I might have created some confusion by talking about bored out carbs that I'd like to try on the 592. But that is in the future. Currently I'm using stock 069A carbs from the 75-77 CB550F. I'm trying to make these work on a highly modified CB550 engine with a Dynoman 592 cc, 10.5-1 compression piston set. A full ported head with matching intake manifolds, a Webcam  358B cam, kipplewhite valve springs, stock valves, Mac 4 into 1 exhaust system and 4-Unipod air filters. Igntion in Dyna 3 with 5 ohm dyna coils NGK plug caps and D7ES plugs

Initially I ran a 110 main jet with needle on 3rd clip down and #40 pilot and needle 1 turn out. This was my baseline setting.(stock is #98main, #38 pilot, needle on 2nd clip, air screw 1.5 turns out)

The plugs were black and fouled relatively early on, bike ran poorly at low speed with stutter and hesitation but would clear up from mid throttle on (was keeping revs below 8,000rpm)

After much back and forth, several test sessions with different settings (see earlier posts) and with good information from the forum, I went back to square 1 and put in a #100main, #38 pilot, needle on 2nd clip from top, air screw at 1.5 turns out. It is difficult to do wide open throttle, through the gears, plug chop tests as I live downtown Toronto and access to an abandoned straight road is probably hours away. So I'm stuck with feeling it out as best I can. Possibly only a dyno run can help at this point or get a couple of friends and go find a secluded road for a day with a load of jets and plugs!!

Currently the bike still has low speed jetting issues where it stumbles and burbles on 1/8 to 1/4 throttle opening. It also burbles at steady throttle with small 1/4 opening. It idles perfectly at 1200-1500 rpm, throttle does not hang up when reved but engine stumbles upon rev in neutral or sitting at a light. It seems like it's choking, wants to rev but can't do it cleanly. When I have a moment to rev it hard (wide open) underpower from about 4000 rpm it will accelerate smoothly and quite hard till about 7000rpm where it will misfire till about 8000rpm at which time it clears up and accelerates really hard till redline (about 10,500) rpm . A plug chop after this shows a still dark plug but more deep brown than blk. Of course this is not ideal but the mystery of the misfire lets me think it might be a touch lean on the midrange and need the needle raised a bit.

[Flying J]

Sounds like your getting closer. Im not looking forward to this part of my build but i know its coming.

[Kemp]

TG - I bought some NGK DR-7ES plugs (restrictor plugs) and my NGK plug caps are for restrictor plugs. I found myself a test road which is basically deserted Sat/Sun as its an industrial area.

Tried a flat out run with the #100 main jet and using the "sligthly used" D7ES plugs (non restrictor). The engine missed fired from about 6000rpm up, didn't clear up. Plug chop showed  a very lean condition, pure white electrode.

Changed to a #105 main jet and added new DR7-ES plugs. The bike ran strongly right through the rev band all the way to 10,000rpm, no misfire. Plug chop from wide open throttle peaked in 4th gear showed a white centre electrode with some light grey color on the sides of the electrode and black on innerside of plug body, greyish white on outside tip of electrode and a grey/tan circle at the base of the electrode. Driving the beast around the area showed slight fluffyness at 1/8 throttle but once over 2500rpm it would take part throttle cleanly and heavy throttle with slight hesitation. Adjusting the air screws to 2 turns out gave a bit nicer slow speed response. Steady idle at 1500rpm with no throttle hang when reved in neutral.

Should I leave it alone! Early on when I had the 110 main installed the plugs were basically all black. They were not restrictor plugs though, just standard D7-ES. I think I might be still a touch lean, not sure if it could cause engine damage from being too lean as It does look close to a good burn. Here again are the current carb settings:

Stock CB550F carbs (069A) with Uniflow Pod air filters (oiled)
main jet #105
Needle jet - 2nd clip from top (stock)
pilot #38 (stock)
float level - 22mm (stock)
Air Screw - 2 turns out (stock is 1.5)

[TwoTired]

R plugs = Resistor plugs.  It that what you mean?

I still think you are trying to do it all at once.  I think you need to find the correct main jet with WOT plug chops and get the proper color on known clean plugs.  Then you have one thing known in the carbs, to leave alone.
Then you can work on the slide needle and futz with the air screws to get closer to happy at throttle positions other than WOT.  It's a divide and conquer strategy.  Not a massage everything at the same time and hope you got lucky.  I'd rather focus on one aspect at a time.

You need to get the main set for best power and still self clean, imo.
This gives you an idea on what to look for:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Cheers,

[Kemp]

Hi TT - Yes, R means restrictor plug in my post, this is a change from the std plug I'd been running. Very nice chart, thanks!

Looking at this chart I'm still a "bit hot or lean but okay". Basically I'm plug #22. I think I'll try a #110 main jet today and see how that goes.

Kemp

[TwoTired]

Hi TT - Yes, R means restrictor plug in my post, this is a change from the std plug I'd been running. Very nice chart, thanks!

It's just a terminology thing. 
R = resistor.  As in, the spark plug is constructed with a resistor inside that operates inline of the electrical current flowing through it during spark.

I just don't feel that restrictor is proper terminology, and have not seen that term applied to spark plugs by the knowledgeable populace.

Not a big deal, really.  But, many people do judge by the words used within conversation.  Perhaps this is why Ebonics is so popular?   

Cheers,

[Kemp]

Ebonics doesn"t apply in this context as "restrictor instead of resistor" was simply a brain fart. Perhaps Idiotonics would be closer and maybe that was the thrust of your dissertation. In either case, I have more fun news.

Looking at your lovely plug chart I have the following notes:

D7R-EA color from yesterdays test was actually very good, upon a second careful reading I would say it is about a #18 on the chart. This was with the 105 main jet

DR8-EA plugs were tried today. The carbs retained exactly the same set up as the test with the D7R-EA from yesterday. Today the weather was a bit cooler and overcast with occasional rain showers, yesterday was more a threat of rain but stayed dry. The DR8-EA plugs I ran today showed more contrast than the DR7s. The center electrode was whiter (abolutely clean) with the electrode tip pure black while the ground electrode was a grey/white color and the surrounding plug casement was blacker. The machine did not run quite as well. It seemed the hesitation and stumble was a bit worse and extended a little higher in the rev band than with the DR7s. It's overall driveability and throttle response was poorer than yesterday. At wide open throttle acceleration seemed flatter in the mid range rpm (4-6000) and similar to yesterday at high rpm (8-10000) although there could be a bit of a slight misfire occurring in the higher rpm band. The color was more like #22 on your chart.

[turboguzzi]

glad to hear the R's helped,

i've seen this happening so many times, i.e. high rpm misfire with non R plugs that i am not even surprised ...

what about the caps? you siad "made for resistor plugs" dont know what it means, caps should have their impedance written on the side, if they have not, then they arent resistor type.....

tell us how many ohms your caps have first

[Kemp]

TG - the plug caps are NGK Resistor covers rated at 5 ohms. Yes using the DR plugs has allowed everything to fall in line properly while the non resistor plugs fouled and gave completely inaccurate readings. A real wake up call to pay attention to the system needs.

I finally have the main jet figured out. Good plug chops(NGK DR-7ES) at peak rpm in 3rd gear. A #120main is the safest choice with a clean fairly white electrode ( some color on electrode, darkish grey to dark brown at curve) a nice grey/tan ground electrode and a light tan color at electrode base. The bike might be a little sharper at high rpm with a #115 main jet but the ground electrode is grey/white and electrode is almost white with a little color(greyish). The bike would pull cleanly on wide open throttle through the high rpm band (7-11,000) with main jets as small as #105 but obviously a little on the lean side. Now I need to get the mid range and low speed dialed in.

At 1/8-1/4 throttle engine hesitates and burbles when throttle is opened. At 1/2 throttle it accelerates cleanly when throttle is opened. Idle is steady at 1500rpm and returns promptly when revved in neutral. Air screws are set at 2 turns out at the moment. At low speed (around town) when attempting downshifts the engine hesitates severely when asked to rev, almost as if it is choking. Not sure if I should raise or lower the needles which are in the 2nd clip from the top (stock). Slow jet is stock (#38)

[turboguzzi]

sounds like raising the needles could help

[Flying J]

My bike has been doing the same thing when i accelerate from a light downshift. It cuts out before it starts to pull again. I put in a 40 pilot and its a little better but i think I'm going to lower the needle a notch and see what happens. But first i think i should also do a  wot plug chop.

[Rick4004]

I've come to the party a little late, but I fully agree with Two Tired. Always get the main jet right first, because it affects all the other circuits. Here's a link to a great jetting article from Factory Pro. http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Good luck Kemp, hope you get the bored carbs installed soon.

Rick Denoon

[Kemp]

Hi Rick, thanks for the jetting guide, very useful and well written. Currently we are just putting miles on the bike to get some break in mileage before I re-torque the head and degree the cam. The plan is put the big bore carbs on right afterwards and get a decent jetting session in before going to the Dyno with both the big bores and the stock units.

[mazen0822]

Hi Rick, thanks for the jetting guide, very useful and well written. Currently we are just putting miles on the bike to get some break in mileage before I re-torque the head and degree the cam. The plan is put the big bore carbs on right afterwards and get a decent jetting session in before going to the Dyno with both the big bores and the stock units.

Kemp any updates on this. Im getting ready do my bike and I have a similar set-up and was wondering if you were able to figure out your jetting.

[Kemp]

Yes, should have finished up this post with my new info. I used a test track (industrial area on weekend!). Worked on the main jet first and simply ran it to redline in 4th gear wide open then did a plug chop. It turned out he beast needed a 125 main jet to get a proper light tan colored electrode. The bonus was that the rest of the carb circuit seemed to fall into place!! The mid range was fine with stock needle position (2nd clip from top) and the slow jet seemed fine with one up from stock (#42).  The air screw ended up at 1.75 turns out from stock. Igntion is a Dyna 2 with dyna 5 ohm coils and dyna coil wires and caps. Carbs also have Uni filters and exhaust is MAC. The bike accelerates like a mad thing with powerband about 7500-12500rpm on my mini tach. Mid range is much like stock bike with the new power way up in the rev band. This is the only disadvantage of the slightly wilder web cam, peak power versis wider powerband, peak power over a more balanced torque/power compromise.  I would suspect about 50 rear wheel hp.

I built a 591 engine using NOS Powerall kit with a 650 cam and Mac exhaust and uni pods. This engine was very flexible with a very strong mid range acceleration and a pretty good top end rush. This engine was way better than stock and would accelerate hard at 80mph in top gear with a top speed of about 110mph at redline. I love this engine because in real world use it's fun and really flexible.

The former 591 engine is definately faster but it's take no prisoners, high rpm serious power in a relatively narrow powerband, great race engine but not so nice street bike.

[MRieck]

What is your cam lobe center?

[Kemp]

I did not degree the cam. although I have a slotted sprocket I simply set it to the stock cam timing marks. I do plan to degree the cam and it may alter the mid range as I understand that the 550's like a 105 degree lobe center with the web cam. Still I doubt it will have the same mid range as the very mild 650cam offers with increased displacement

[MRieck]

Time the cam....it make s a big difference

[Jim F]

Let me tell you about getting the cam timing right.................
very important to start there and make sure about your lobe centers are correct 
BEFORE you do any kind of tuning

good luck

[Bill/BentON Racing]

Degree the cam,start with main jet...ALWAYS,Two of the Engine 10 Commandments according to........me....my .02.Good Luck,Bill

[specweld]

had this problem a few years back,just dropped the needle by one notch ,problem gone.
you have bigger opening in main jet but needle is still  in the same position, so you now have more space around the needle therefore more fuel coming in which probably accounts for the rich running and baulking on low throttle.
dropping the needle will close the gap between itself and the main jet and should weaken it off at low throttle settings but doesn't alter anything as you open the throttle more.
worth a try.. and it worked for me.

btw. not too sure about running 7's (plugs) on a perfomance engine, I once holed all four pistons using them but that was racing in the Isle of Man where you can be thottle wide open for long periods.

 

[Kemp]

I now have the 591 back in my possession and hopefully get to it by mid next week. This will be my first shot at degreeing the cam!!