PH BB Mechanics, help me!

[VidalBaboon]

Help me diagnose my poorly 7R.

Poor running below 4krpm, wind the throttle on and it gets worse, to the point of cutting out. It then won't start for a few minutes (wet plugs at a guess). Once it fires up, you have to hold the throttle at a certain position till it revs cleanly through.

Once this has happened, you have to clutch it up past 4krpm and it runs fine.

I pulled my carbs apart hoping it was something simple, but nothing obvious apart from Dynojet needles and ever so slightly ovaled needle jets. I put the needles on their leanest settings but no joy, so I took the carbs off and put a second hand standard set on. It's still doing the same thing.

Assuming I've ruled out fuelling by fitting a different set of carbs, next up is the ignition system. I've got a pulse pick up coil, loom and CDI waiting to be trialled.

Am I missing anything glaringly obvious? Perhaps check the reg/rec- see if it's giving the CDI enough juice at low revs, split inlet rubbers (they did look alright, but it was only by glancing at them - gets a bit tedious taking the carbs off every 5 minutes)


Please help!

[VidalBaboon]

Nobody likes a split rubber. They looked good to me when I pulled them off, but will check again.

Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??

[VidalBaboon]

No I don't think so, I did a float bowl mod (equalised the pressure between float bowl vent and airbox) but it ran exactly the same. So I've decided to go from square one and put it all back to standard.

[VidalBaboon]

Yazza54 said:

VidalBaboon said:

Nobody likes a split rubber. They looked good to me when I pulled them off, but will check again.

Shirley a split rubber would cause the fueling to get progressively worse as the vacuum increases with raised engine revolutions??

Surging can make a motor run all sorts of rough, do the revs hang before decreasing when you let off the throttle?

Have you rejetted after fitting your new exhaust system?

Have you done anything to the breathers?

No they don't hang, thinking about it I have noticed a delay when blipping the throttle on downchanges (8-10k), there's sort of a split second delay which isn't apparent at low revs (5-8k).

The bike runs huge mains to compensate for the air recirc system on the exhaust. The bike was originally running mains suitable for a snazzy system but it made no difference having Keihin 180 mains or Dynojet 132 mains. Having the jets slightly out would never make it run this bad anyway, flatspot yes, but not this bad.

Edited by VidalBaboon on Monday 14th May 22:08

[VidalBaboon]

All 4 plugs are fouling, assuming I've ruled out any fuelling issue wih swapping the modded carbs for a standard set (the guy that's put the carbs in used to be involved with racing 7Rs in the 90s, so guessing he has a better idea of well set up carbs than me)

the only other thing that affects all 4 cylinders is the ignition, or as you say, a pesky air leak.

[VidalBaboon]

Tried a different set of spark plugs. Not bothered checking the continuity of the HT leads and plug caps yet as it's affecting all 4 cylinders, not just one or two (2 as it's got twin coil packs).

[VidalBaboon]

Dynojet sizes are different to Keihin, and it has the emissions ste back on to lean the mixture out (somehow, black magic I assume).

You can (apparently) run an aftermarket system on standard jetting without any 'major' problems, I certainly had no issue swapping between standard and open can on the last one. If it was a jetting issue, it would have been cured by fitting the new exhaust.

Edited by VidalBaboon on Monday 14th May 22:23

[VidalBaboon]

Fleegle said:

Does it have an inline fuel filter?

If so, when was it last changed?

It's not starving of fuel. Filter looks good, no crud in the tank either.

[VidalBaboon]

Yazza54 said:

Oh good haha. Still, which ones?

It's running standard carbs with the emissions stuff back on. I have tried to put it back as standard as possible to fault find.

[VidalBaboon]

Yazza54 said:

VidalBaboon said:

No I don't think so, I did a float bowl mod (equalised the pressure between float bowl vent and airbox) but it ran exactly the same. So I've decided to go from square one and put it all back to standard.

Reet, read this (if you havent already) http://homepage.ntlworld.com/webzxr/zxr750r/Featur...

With your mod it sounds like your jetting may now be too rich which would explain the plugs fouling.

If it was jetting, it should have been cured by fitting the Muzzy system with the stage 1 dynojetted carbs. I thought exactly the same hence buying the exhaust, but this hasn't worked

I did the mod in the link above too (did it on the last one too), but it's all back as Kawasaki intended at present. Fault finding with modded bits is a bd

[VidalBaboon]

CQ8 said:

VidalBaboon said:

I thought exactly the same hence buying the exhaust, but this hasn't worked

I told you it wouldn't! But you had to have the bling..

It was an educated guess

[VidalBaboon]

Yazza54 said:

But what is the dynojet setup? What is it to be used in conjunction with? Are dynojet jets bigger or smaller than the keihin ones?

ETA:


Kehien Jets -------- DJ Jets

Num / Thou. ------- Num / Thou.
92.5 / 0.035 ------- 92 / 0.035
95 / 0.036 ------- 94 / 0.036
97.5 / 0.037 ------- 96 / 0.037
100 / 0.038 ------- 98 / 0.038
102.5 / 0.039 ------- 100 / 0.039
105 / 0.040 ------- 102 / 0.040
107.5 / 0.041 ------- 104 / 0.041
110 / 0.042 ------- 106 / 0.042
112.5 / 0.043 ------- 108 / 0.043
115 / 0.044 ------- 110 / 0.044
117.5 / 0.045 ------- 112 / 0.045
120 / 0.046 ------- 114 / 0.046
122.5 / 0.047 ------- 116 / 0.047
125 / 0.048 ------- 118 / 0.048
127.5 / 0.049 ------- 120 / 0.049
130 / 0.050 ------- 122 / 0.050
132.5 / 0.051 ------- 124 / 0.051
135 / 0.052 ------- 126 / 0.052
137.5 / 0.053 ------- 128 / 0.053
140 / 0.054 ------- 130 / 0.054
142.5 / 0.055 ------- 132 / 0.055
145 / 0.056 ------- 134 / 0.056
147.5 / 0.057 ------- 136 / 0.057
150 / 0.058 ------- 138 / 0.058
152.5 / 0.059 ------- 140 / 0.059

TAPER of the DJ needle is much thinner than stock needle

Edited by Yazza54 on Monday 14th May 22:54

In conjunction with K&N and open system. Both were fitted and it still had the same problems. It still has the same problem with a standard set of carbs on, which leads me to think it's not fuel related, apart from as suggested, an air leak.

[VidalBaboon]

Yazza54 said:

Hmm I just don't think it sounds like an ignition problem. The fact you said it gets worse with more throttle suggests something is wrong with the mixture, to me it does anyway. I may be wrong. Id be looking for any dodgy gaskets or split rubbers for a definite though.

It does. It almost went away when it was baltic cold in February, which would also suggest that it was running really rich. However, a bog standard set of carbs hasn't cured it.

Tis a weird one.

[VidalBaboon]

kev b said:

I know the carbs have been swapped over to no effect but are you sure the choke is not sticking on? Have you tried finding an air/ vacuum leak with carb cleaner or WD40? Is the air filter element blocked, wet or oily?

swapped air filters over, cleaned and oiled the K&N, it's all made no difference.

I take it finding a leak with WD is just a case of it running like a dog when it ingests it?

Never tried it to be honest, it's all be visual.

[VidalBaboon]

I can't see the inlets with the carbs fitted, I'll have to take them off.

[VidalBaboon]

Last week

I did the float bowl vent mod but it made cock all difference, worth checking the reed valves though. Thanks for the offer Pete but ill pass

[VidalBaboon]

Its like redmonkey in here!! Ku-kaw

[VidalBaboon]

Its sat on my kitchen table That i destroyed with carb cleaner Last week

Will be trying it tomorrow

[VidalBaboon]

You're killing me Fleegle

[VidalBaboon]

jackthelad1984 said:

Buy a newer honda,problems solved!!

Wash your mouth out! Even your neighbors don't like Hondas