Coil resistance?

G

GTCarlos

New member
Location
Sunny Oakland, California, USA
Hi All,

I have a dead stock 7/84 RGS. Since I got it with about 5500 miles on the clock, it has never run well. hard starting, dodgy power below 3500 RPM, etc.
Recently I rolled it out for a ride and it wouldn't start at all. Being fed-up, I finally dug into the carbs to see what was wrong and after a few jet changes it starts fine but will barely stay running below 2000 RPM. -Which generally makes it a pain to ride. I'm tinkering and further diagnosing the problem now, but part of what I thought I'd update are my coils, plugs and wires.

After reading the Nov. 6, 2009 thread (etc), I found some cheap generic coils (that were supposed to be TEC spec.) to replace the Motoplats that are on my bike. The seller had no idea about the coil's specs but I went ahead and ordered them. When they arrived I found they have 3 ohm primary resistance rather than the 5 ohms of the Motoplats. No idea of the output voltage.

I'll run them with multi-strand, non-resistor Cu wire, NGK 5 Kohm caps and B8ES plugs. My question is, is there any problem with using the 3 ohm coils? Will I end up with a dead battery or a dead engine after a ride?

Thanks for your experience, advice or / and educated guesses.

Best regards,

-Danny
 
3 to 3.3 Ohm is oem coil specification, you did well to be rid of the Motoplats they are not good at all. Reads like you have the original Bosch BTZ ignition modules? If so the 3 ohm primary DC resistance coils will drive the BTZ a little harder, though in the long term, new ignition will solve a lot of the cold crank start issues, and your plugs will last 10K miles. Lots of help here free for the asking, and you did well to do a search first... hope that helps, Danny , j
 
As John (iis_iis) says 3ohm coils are fine and no they won't flatten your battery.
Motoplat coils are renowned for poor running.
 
And, honestly, think about changing the Bosch ignition to something nicer ;). You won't regret it.

I guess you're not still making your system, John? In which case, Witt would probably be my choice.

But have a look here, Danny; and, seeing as you're in North America, contact Wolfgang Haerter in Canada for his recommendation.

BreganZane - Live Laverda!

www.breganzane.com www.breganzane.com
 
So in theory with the new coils and plugs, ht leads, caps along with the right jetting and clean carbs...and only 5500 miles...it should start and run good. EXCEPT with original elec. ignition the transition to full advance is abrupt at just the RPM you want cruise at so moderating throttle in that range is a pain. Also plugs don't seem to last as long and easier to foul. That being said, the bike should run ok and be useable unless something else is not right like plugged carbs etc. As suggested a new ignition is the way to go and would eliminate the the biggest reason for poor low rpm performance.
 
Hi Laverdisti,

Thank you all for the guidance in sorting out my bike. The "get a modern ignition" message was received loud and clear. It's now officially on my schedule for when the budget catches up. Meanwhile, I have cleaned and re-jetted the carbs, fitted the new coils, wires and caps and tonight I'll pick up some plugs, install them and put the critter back together with my fingers crossed. I'll check back in the next few days with a report.

Based on the rave reviews from my friends with those Other Italian bikes from Bologna, I'll probably go with a Sachse system, pending further research.
 
Remove the anti start resistors on top of the ignition coils if still retained, the BTZ puts out around 15KV at the the plugs, cold crank start on fuel enrichment requires 25KV for reliable start. The TEC coils are rated at 25KV, the losses ( 10KV ) is due to the BTZ modules.

Bosch, may even enjoy the unburnt fuel in the exhaust system igniting the odd time a BTZ supplies a spark, one of my customers kids missed the start ritual on dads RGS, blue flames and massive bang... BTW why are you rejetting? Mains about 118, 65 pilot is due to the one step BTZ over fueled to mitigate the gross pinking and jerking engine at around 2000-2500rpm. Proper ignition and 55 pilot will achieve decent fuel mileage out of a tank, oh and move the battery negative high current feed from frame to start motor frame. HTH j.
 
Greetings All,

Well, I put the RGS back together last night with the new coils, wires, plugs and caps installed. It has been re-jetter to "stock" i.e. 65 pilot and 118 mains - I didn't check the needles and slides on the rash assumption that no one ever had any reason to change them. Charged up the battery and gave it a start this a.m....

No Joy:
Fully choked, the bike fired right up -which was a big improvement. I feathered the throttle to keep it running and after a half a minute or so, rode off up the hill. The bike barely stays running below about 3500 RPM and doesn't really run consistently until 4,000. It seems to run OK above that but even then it "coughs" through the pipes occasionally. I put about 6 slow miles on it in my hilly neighborhood. Even warmed up it barely runs below 3,200, requiring quick throttle work and abck to full "choke". There's not even a suggestion that it will idle although the idle adjuster isn't even touching the stop on the throttle linkage. -One thing at a time.

So does where do I go next? Back to carbs? valve clearances? Is now the time to spring for a new ignition system to replace the BTZ that's in there? Nb; The bike sits most of the time but it ran badly but better until recently and b. I see no evidence that the fuel supply is a problem.

Your collective experience greatly appreciated as always.

Best,

-Danny
 
And further details...

The battery is still grounded to the frame but I'll change that. Thanks.
The P.O. had messed with the jetting so the bike was always hard to start and notchy. After messing with it a bit as he had it, I ordered in some jets and eventully reverted to the "stock" set-up. I'll try 55 or 58 pilots (whichever I have on hand) when I look at it next.
The plugs that came out were pretty evenly dark but not fouled "looking".

-Danny
 
The total effective air gap ( TEAG ) on the failure prone ( if not the wiring degradation it is the pole faces "pulling" out from the molded body ) bosch pickups will need to be close or less than 0,25m/m for the Total Air gap ie there are two pole faces that add up magnetically for the TEAG setting.

The wider the TEAG the later ( higher rev ) its one step 32DBTDC is pulled. Caveat in this being a reluctance to run at pilot jet to needle transition is pointing to the carbies, start with 65 on the "idle pilot jet", fuel mixture screw out a minimum of 1 3/4 on all carbies ( further out to get a non lean mixture at idle ). Some of this has been covered previous on this forum, others with dab quick hand memory will locate perhaps.

We ride them, we fix them... just started a rebuilt motor yesterday, got it to idle fairly quickly, experience counts for a lot, at times..... oh make sure the fuel tank vent and overflow tank hose are not kinked, or blocked. HTH j.
 
So,where do I go next? Back to carbs? valve clearances?.


When I bought my Jota new '79 it ran fine for the first 3 months. On a trip from Adelaide to Canberra with a mate on a BMW, my bike would not start after a fuel stop in NSW. After many attempts to start it up with warm engine, we decided to go for a "tow" start. Rope tied to the back of his BMW, through the forks and around the l/h handlebar of the jota. Off we go me in second gear clutch in at 40 kph dump clutch keep towing wouldn't start. Tried again with full choke on, fired up and ran on full to half choke only. Would not run under 3k at all without choke. Anyway had to tow start from cold each day and it would start and run on full choke when hot but not under 3k very well. Had to have some choke on. Turned out my valves had recessed to almost zero valve clearance "soft head". Warranty job reinstating valve clearance cured the problem instantly. Not saying this is your problem but the symptoms seem similar.
 
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I was going to suggest cam timing (apols if it's been covered already) - similar symptoms to BJ''s negative valve clearances (above). Has the cam timing been checked and is absolutely correct? I doubt very much carburation could be that far out. There's another issue at play here.
 
Check slides and needles. I spent 4 months messing around with a 750 until it was found that it didn't have the right needles. In the present case, it stuttered as from 2000 revs.
It sounds as if your bike isn't fed through the idle circuits.
Paul
 
RGS head won't suffer soft head syndrome, but checking and adjusting valve clearances is a necessary part of setting up a bike to run properly. Valve timing marks are easily checked when the cam cover is removed.(I appreciate this doesn't guarantee correct timing if someone has messed with cam wheels!)

As Paul says, this sounds like blocked idle circuit drillings in the carb body. If you haven't done so already, then check as described here - 'pilot blockages'
https://laverdaforum.com/resources/stevios-hintsntips.82/

And also check correct slides and needles.

Finally check and adjust float heights.
 
It might not be what you think, which is a need for more fuel at low revs and hence opening up the choke again to keep it going.

I would look closely at the float valves and their tips and seats, are the tips black??? they should be pink, new sets are cheapo, easy to install and I always use 300 size (250 is stock) since when at high speed and getting near reserve you will still keep the float bowls full until you are actually needing reserve, so go for a set of 300's, be carefull with the existing tiny fibre washers under the seats, and also check the float levels at the same time. (18.5MM)

Just another thought, have you have the tank pet cocks out and checked the filters? likewise the three filters under the banjo's on the carbs?
CLEM
 
CLEMTOG said:
It might not be what you think, which is a need for more fuel at low revs and hence opening up the choke again to keep it going.

I would look closely at the float valves and their tips and seats, are the tips black??? they should be pink, new sets are cheapo, easy to install and I always use 300 size (250 is stock) since when at high speed and getting near reserve you will still keep the float bowls full until you are actually needing reserve, so go for a set of 300's, be carefull with the existing tiny fibre washers under the seats, and also check the float levels at the same time. (18.5MM)

Just another thought, have you have the tank pet cocks out and checked the filters? likewise the three filters under the banjo's on the carbs?
CLEM
Click to expand...
Fuelling at low revs is the idle circuit if it ain't going through the enrichener, not choke. Enrichening at low revs is what this machine needs apparently.
Paul
 
Well, the plot thickens...
Last night I made my way to the garage just to check on the TEAG, which, if I understand correctly, is the combined gap between the 2 pick-up "contacts" and the rotor magnet.

It seems the outer pick-up is actually HITTING the rotor, on all 3 sensors. The inner "contact" seems to have clearance but I couldn't measure it with the tools I had at hand. What's more, the wire insulation on at least two of the pick-ups is crumbling exposing (not yet corroded) bare wire. Since those affect both when and if the plugs fire, it's amazing it is running at all!

Question 1:
Am I right in thinking that the COMBINED gap of the two sensors should be ≥ 0.25mm? If so, does it matter how that's split front to back?

Question 2:
How the %^& do you adjust the gap? It *seems* that the head of the allen bolts that secure the sensors butt up against the plastic part of them so that they CAN'T be pushed back to provide clearance for the outer "contact". Short of some convoluted shimming that I doubt would hold even if I did get it to work, I can't see any way to adjust the gaps.

IS this a fixable issue or should I just scrap the whole system and replace it? I wrote Wolfgang Haerter last night about a new ignition system but haven't heard back yet.

TIA for your thoughts.

-Danny
 

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