Author Topic: Stuttering under part-throttle (Read 22845 times)

E30_Crazy · « **on:** May 12, 2017, 05:53:41 PM »

Brick in question is an 85 K100 2V.

Usually fine up to around 4k RPM, then I get some hesitation under part throttle if cruising or slightly accelerating. Can most of the time power through it, on up the RPM range at full throttle. Every once in a while, it will stutter all the way up.

Just looking for the next logical step.

I've changed the plugs and wires, and coil checks good to specs. Taken a torch fuel bottle and sprayed around the throttles and other rubber to check for a rise in idle (none).

I have recently replaced the FI computer and the AFM.

Next on my mind is the fuel filter. But other possibilities I can think of, and/or read about are injector reconditioning, FPR and lines, coolant temp sensor (may be getting rich/lean mix if this is putting out wrong resistance, I believe), and possibly attempt a TB sync.

Anything else I might be forgetting, or other opinions on what to tackle next?

Scott_ · « **Reply #1 on:** May 13, 2017, 09:33:40 AM »

I'd suggest you check valve clearances before a TB sync if you haven't recently.

The Mighty Gryphon · « **Reply #2 on:** May 13, 2017, 10:11:55 AM »

Are you using made in India Bosch plugs? Someone on another forum had starting problems that went away when the made in India Bosch were replaced with NGK. Your stuttering sounds like intermittent spark, and could be one or more plugs.

If you go NGK, you will need the terminal nuts at the top to get a correct connection to the OEM plug wires. You can get them from NGK customer service. Just email them, and they will send them to you, no charge.

E30_Crazy · « **Reply #3 on:** May 13, 2017, 04:52:45 PM »

I'm already running NGKs with the terminal nut on top. Guess I need to get some feeler gauges and check valves. I did recently change out a cam that had snapped on me. But it ran fine for a while after that.

E30_Crazy · « **Reply #4 on:** May 13, 2017, 07:35:14 PM »

Pulled the fuel filter today. Cleaned it out best I could, shook it up with some fuel inside, drained, hooked it up backwards and ran the fuel pump (fuel into a jar, of course). Repeated several times until mostly clear. Thought I might have fixes it, but after a few miles the stuttering came back. So either, the inside of the filter is falling apart and I just need to be patient and wait for a new one, or it's temperature related. Gonna try and test the temp sensor without burning myself on the radiator tonight. Or it could be a by-product of heat on an undiscovered cracked vacuum hose (once warmed up, more flexible, hole/crack then allows air in)

The Mighty Gryphon · « **Reply #5 on:** May 13, 2017, 07:41:07 PM »

Why are you messing with the fuel filter? The crap that stops the flow is trapped in the paper and can't be flushed out. Back flushing also messes up the element.

Go to NAPA and get a #3032 NAPA Gold. 5/16" line, steel can inline filter. Less than $5.

Elipten · « **Reply #6 on:** May 13, 2017, 08:58:19 PM »

My thought exactly. Too cheap to do anything but replace.

Sent from my iPhone using Tapatalk Pro

E30_Crazy · « **Reply #7 on:** May 15, 2017, 05:24:29 AM »

I'll have to do that... After I get a new injector. I had some seals, tips, and microfilters to do a soft-rebuild. And not thinking too clearly, when seating one of the microfilters in the top, I had the tip on the counter.... Without the yellow tip on... I mashed over the little pimple that protrudes out the end of the injector... So now gotta buy a new one...

On that note, should I just go ahead and buy a set of the 4-pintle injectors? The ad claims better throttle response and MPG. Remanned from standard, of course.

Motorhobo · « **Reply #8 on:** May 15, 2017, 06:26:53 AM »

Which 4-pintle ones are you talking about? I'm looking at the ones here:

For my K75:

http://www.jt-c.com/product_info.php?info=p35_k75---4-holes-injector-upgrade.html

For your K100:

http://www.jt-c.com/product_info.php?info=p4_k-upgrade-2v-and-4v---4-pcs.html

Then there's this:

http://www.jt-c.com/product_info.php?info=p40_k100---k1100---k1200-tuning--25-.html

Let me know if you've got something better cheaper in domestic production...

E30_Crazy · « **Reply #9 on:** May 15, 2017, 07:54:38 AM »

These are the ones caught my attention. And on sale currently. Much cheaper than ~130EUR.

http://www.ebay.com/itm/BEST-UPGRADE-Genuine-BOSCH-Fuel-Injector-Set-of-4-Update-4-Nozzle-Tip/281435347207?_trksid=p2481888.c100675.m4236&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D6b4f69d9087a4894bd698d14b8cd877c%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D281435347207&_trkparms=pageci%253Aa79fa650-3964-11e7-a692-74dbd1804fea%257Cparentrq%253A0bf1c4a215c0ac8077b255fcfffe1311%257Ciid%253A1

Motorhobo · « **Reply #10 on:** May 15, 2017, 09:00:02 AM »

Cool -- thanks, I think I'll join you on that!

Filmcamera · « **Reply #11 on:** May 15, 2017, 09:08:00 AM »

If you do I would be very interested to hear how they are different and what performance gains you get.

The Mighty Gryphon · « **Reply #12 on:** May 15, 2017, 09:34:46 AM »

I too, would be interested in hearing what improvements are gained.

The listing claims smoother idle, better atomization(how does a user determine that?), better throttle response(MAF lag is the problem there), and easier starts.

Probably no improvement to be had on my bikes. They start instantly and purr right from the start. Can't tell how they atomize, but judging from the way my bikes run and the 45-48mpg I am getting the old injectors are getting the job done.

Throttle response on Jetronic equipped engines is determined by the inertial lag of the MAF sensor's "barn door". Removing it in favor of a throttle position sensor in the Motronic system is the reason for the MUCH crisper throttle response of the 4 valve engines.

Downside of the four hole injectors is that the injector orifice diameters are 1/2 that of the single hole injectors. In my book, being the mechanical pessimist I am, that means they will be at least twice as likely to plug and create problems with fuel delivery.

Motorhobo · « **Reply #13 on:** May 15, 2017, 09:51:53 AM »

I just ordered them -- we'll see. The injectors on my current rider are 178k miles old it's either have these cleaned or get new ones, so new ones it is, at that price can't be worse than what I've got.

Well see about the green, though...

E30_Crazy · « **Reply #14 on:** May 19, 2017, 08:12:56 PM »

I procrastinated too long and just ordered mine the other day. So now they won't be here for the weekend. Oh well. Have you gotten yours yet? I wouldn't mind seeing pictures of the actual injectors, since the eBay store seemed to use stock photos.

jakgieger · « **Reply #15 on:** May 20, 2017, 12:00:00 AM »

These look to be the same injectors I got from Osidetiger on Ebay...I saw 10+ mpg and 20 more hp :hehehe :hehehe . No, seriously, I never ran the pintle injectors (bike had sat for 10+ yrs.). I will say that power and throttle response are good. Don't have any reading on efficiency. Replacement is direct...MG, you're right about hole size, BUT, change your filter regularly with a quality product.

Motorhobo · « **Reply #16 on:** May 20, 2017, 07:44:36 AM »

Quote from: E30_Crazy on May 19, 2017, 08:12:56 PM

I procrastinated too long and just ordered mine the other day. So now they won't be here for the weekend. Oh well. Have you gotten yours yet? I wouldn't mind seeing pictures of the actual injectors, since the eBay store seemed to use stock photos.

They look as advertised -- but are considerably heavier than the OEM ones, from what I remember. Looks like there is actual metal to these, where I remember the OEM ones to be 100% plastic.

These are the ones at the eBay link above:

http://www.ebay.com/itm/BEST-UPGRADE-Genuine-BOSCH-Fuel-Injector-Set-of-4-Update-4-Nozzle-Tip/281435347207?_trksid=p2481888.c100675.m4236&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D6b4f69d9087a4894bd698d14b8cd877c%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D281435347207&_trkparms=pageci%253Aa79fa650-3964-11e7-a692-74dbd1804fea%257Cparentrq%253A0bf1c4a215c0ac8077b255fcfffe1311%257Ciid%253A1

I'm going to ride a bit this morning, do the install, sync the throttle bodies, ride a bit more and will report back...

E30_Crazy · « **Reply #17 on:** May 20, 2017, 09:04:04 PM »

Oh wow. Just got mine today. Didn't think they'd be here for the weekend. I'll have to go grab one of those replacement fuel filters tomorrow. It's very tempting to throw them in tonight, but no sense in gumming up new injectors if my filter has failed.

E30_Crazy · « **Reply #18 on:** May 21, 2017, 12:31:01 PM »

Also, after reading about syncing the throttles, I noticed that my caps for the vacuum ports have been switched out for vacuum lines and T-fittings, connecting all of the throttles together. Logic says this wouldn't cause a problem, since it was running fine before (unless there's a split in one, obviously) I mean just in theory of operation.

Motorhobo · « **Reply #19 on:** May 21, 2017, 03:15:36 PM »

Just installed mine and first impression is: awesome. I rode it before the throttle sync and it seemed to be a great improvement -- am going to ride it again now after the sync...of course, the mind plays tricks but...that appears to be $79 very well spent.

BTW they are no heavier than the original ones, my earlier comment was false.

I don't see how replacing the caps and the vacuum hose with t-fittings can be a good thing. If it were me, I'd drop the few pennies on the caps and get that one vacuum hose on the far right with the protector coil around it and do it the way the Krauts designed it -- that is unless someone has a really, really good reason to not do it that way.

Scott_ · « **Reply #20 on:** May 21, 2017, 07:20:07 PM »

I have all of my sync ports connected together with "T"'s to feed vacuum to my Cruise control setups. I've not noticed any performance issues with this setup.

E30_Crazy · « **Reply #21 on:** May 21, 2017, 07:37:21 PM »

Well, no change in the stuttering... Almost feels a little worse now. Can really power through it now. Stutters even with full throttle, and gets hung up around 5 or 6k. Almost starting to remind me of when the ECU failed. Hope it's not that, since that'll make me think there's a bad wire somewhere frying them. Or maybe just got unlucky twice? Still gotta finish checking the rubbers. Haven't got the intake manifold off yet to check the throttle rubbers. Can't very well see the back side of them. Fronts don't look too bad.

Next only list is the FPR and associated lines I guess.

Laitch · « **Reply #22 on:** May 21, 2017, 07:57:32 PM »

Quote from: E30_Crazy on May 21, 2017, 07:37:21 PM

Well, no change in the stuttering...

You haven't mentioned whether you changed the fuel filter. You stated on May 20 that you intended to change it today.

Motorhobo · « **Reply #23 on:** May 22, 2017, 05:50:16 AM »

Quote from: Scott_ on May 21, 2017, 07:20:07 PM

I have all of my sync ports connected together with "T"'s to feed vacuum to my Cruise control setups. I've not noticed any performance issues with this setup.

Thanks -- I didn't know there was a practical use for that. Is that cruise control documented here? I'd like to check it out if it's K75 applicable -- a search for 'cruise control' turned up a number of hits, not sure which is the one that applies.

Scott_ · « **Reply #24 on:** May 22, 2017, 07:00:01 AM »

Quote from: Motorhobo on May 22, 2017, 05:50:16 AM

Thanks -- I didn't know there was a practical use for that. Is that cruise control documented here? I'd like to check it out if it's K75 applicable -- a search for 'cruise control' turned up a number of hits, not sure which is the one that applies.

http://www.motobrick.com/index.php/topic,434.0.html

I have the older vacuum version that you may or may not be able to find new any longer. They have gone full electronic/electric actuator in leu of vacuum.

News:

Author Topic: Stuttering under part-throttle (Read 22845 times)