Help: PZ30 engine requires twisting throttle to start

[AresROC]

Symptom: Engine requires opening throttle to start, hot or cold

Conditions:

• Without throttle, engine would start and then dies quickly
• Cold starts on half choke. Would not start on full choke.
• Idle is set to 1500~2000 rpm.
• Fuel mixture screw tuned to 1/2 turn out for highest idle RPM
• Pilot Jet 35 (Down from 40 & 38. Stock is 34)
• Main Jet 110 (Stock 105, also tried 115)
• Occasional backfire when closing throttle

Additionally, when engine is hot after WOT runs, engine would not quickly return to idle, and instead the RPM would only slow down gradually, indicating running rich?
It is the same problem with no choke also... Any ideas I can try?

ps. I think it might be my fuel mixture screw profile...

[JerryHawk250]

Have you adjusted the valves lately? Sounds like tight valves.

[franque]

Your pilot jet is the wrong size if it's only a half turn out. That, and not starting on full choke are both indicators of the wrong pilot size. I'd also check for air leaks on the intake and exhaust, and possibly also at the EGR. Check the valves first though, do things one at a time.

[AresROC]

Fine things to try thanks!


Yes as a matter of fact I did adjust my valves recently. They were tight and I had to loosen them to spec. Guess I better check again for gap/TDC.

[franque]

If your valves are good (assuming the motor was completely cold when the valves were adjusted?), start looking for air leaks. I'd spray some carb cleaner around the intake side of the motor (when running) and see if it idles up.

I might also try screwing in the idle screw to see if raising the idle speed helps. Also check the filter, connections between the filter and engine, make sure nothing is pinched, but also not loose on the intake side, and as a last resort on the intake side, you could check to see if the O-ring is completely flat between the motor and intake. Also, sometimes the intakes warp if overtightened.

I'd also double check the plug to see if it's rich. Check the EGR system and block it off, as needed. Also make sure the exhaust isn't leaking, and that choke on is the correct position that you think it is. Usually on PZ30s, if I remember correctly, all the way down is choke off.

[AresROC]

Originally Posted by franque

If your valves are good (assuming the motor was completely cold when the valves were adjusted?), start looking for air leaks. I'd spray some carb cleaner around the intake side of the motor (when running) and see if it idles up.

I might also try screwing in the idle screw to see if raising the idle speed helps. Also check the filter, connections between the filter and engine, make sure nothing is pinched, but also not loose on the intake side, and as a last resort on the intake side, you could check to see if the O-ring is completely flat between the motor and intake. Also, sometimes the intakes warp if overtightened.

I'd also double check the plug to see if it's rich. Check the EGR system and block it off, as needed. Also make sure the exhaust isn't leaking, and that choke on is the correct position that you think it is. Usually on PZ30s, if I remember correctly, all the way down is choke off.

Thanks a lot of good points. I recently also upgraded to NGK Iridium plug will check it. The secondary air inject is plugged, with the associated vacuum lines caped. On the PZ30 down is off, and all the way up is full choke. I may also reinstall the original fuel mixture screw to see if that makes a difference.

[JerryHawk250]

Make sure you don't have a resistor plug with a resistor wire cap. That will cause weak spark issues.

[AresROC]

Originally Posted by JerryHawk250

Make sure you don't have a resistor plug with a resistor wire cap. That will cause weak spark issues.

Ooops! That is a problem I got the DR8EIX instead of D8EA... Guess I will be doing a spark plug mod soon!

[NzBrakelathes]

Air screw should be out 1.5 to 1.75 turns estimates and the back fire n close throttle says its lean.
38 pilot is Ok and correctly adjust via mixture screw NOT random tunrs out.

[AresROC]

Well, the DR8EIX spark has a 4k ohm resistance. Was unable to remove the resistor so old Torch D8 had to go back in. After a few cranks bike starts without throttle input no problem. Idles with no choke and half choke, still won't run with full choke (almost no air).


The new fuel mixture screw's tip is very pointy vs the old screw, so I guess the old one is going back in soon.


Spark plug looks on the lean side, maybe because of cold weather.

[Megadan]

Originally Posted by AresROC

Well, the DR8EIX spark has a 4k ohm resistance. Was unable to remove the resistor so old Torch D8 had to go back in. After a few cranks bike starts without throttle input no problem. Idles with no choke and half choke, still won't run with full choke (almost no air).


The new fuel mixture screw's tip is very pointy vs the old screw, so I guess the old one is going back in soon.


Spark plug looks on the lean side, maybe because of cold weather.

That plug shows you are very lean.

If you are using one of those thumb screw mixture screws, yes, they don't really work. That tip profile is important. When I tried to use one I ran into all the same problems, and eventually the tip just broke off. I had no choice to install the original mixture screw, and all of my idle and start issues went away. Put the normal mixture screw back in and get yourself the proper adjustment tool - nzbrakelathes sells one that works, he even had one with him when I met him to grab the forks a while ago.

Keep in mind that for every 25 degrees of ambient air temp, it will require about 1 size increment increase in jet with the keihin jetted carbs. If you were running perfectly at 75 degrees with a 115 main, then at 50 you should be considering jumping to a 118. Then again around 25 degrees a 120.

With the pilot jet the same basic rules can also apply, but it doesn't quite work the same. My rule of thumb with those is if I go beyond 2 turns out, I will bump up a size (if I have a 35, then I go to a 38). It usually takes a much more drastic swing in air temp for pilot jet size changes to be necessary, but it does happen.

[AresROC]

Thank you Dan as always, super informative.

I think the plug has a bit of detonation, and I got some oil burn as the oil level is 1/3 qt short.

Below are the fuel mixture screws. Dirty one on the right is stock. Unfortunately Tako's 90 degree tool can't reach it I will be making my own tool for it soon.

[NzBrakelathes]

When I rode your bike all was well - I also had the air mix screw tool with me! which you mentioned things when I was at your place in Vegas!

So what is it you need? Maybe send the wee list n see if I can help.....

[Wild Dog]

You may have a vacuum leak somewhere but while you are at it, why no change the PZ30 for a PWK. To be honest i loved the PWK more than the PZ30B.

Also take note that those fuel mixture screw you have there have, the tip have profiles that are quite different from the one that came stock.

[NzBrakelathes]

Originally Posted by AresROC

Thank you Dan as always, super informative.

I think the plug has a bit of detonation, and I got some oil burn as the oil level is 1/3 qt short.

Below are the fuel mixture screws. Dirty one on the right is stock. Unfortunately Tako's 90 degree tool can't reach it I will be making my own tool for it soon.

Tool can reach - we didn't try much at all.....

Also you have the Harley 883 written in Chinese on the packet.
You're Chinese/Taiwanese so you could read that, I just recognize the character for Ha and 883 being a Harley engine size.
Seems you don't have a PZ30 screw but some other Keihin?

So hows my Chinese readoing skill??